Master Plumber Exam — Questions and Answers

Question 1: Which of the following fixture types can be served by a waste and vent combo system?

Bidets
Urinals
Sinks (Correct answer)
Toilets

Correct answer: Sinks

When using CWV systems, not every fixture needs to have an individual vent. The fixtures that have been approved for a CWV installation have bigger drains installed instead of a vertical vent. The fixture obtains the necessary air for drainage in the upper section of the bigger piping because the drain diameter is greater. Toilets, bidets, and urinals cannot be put on CWV systems.

Question 2: According to the IPC, what is the maximum developed length for a fixture drain from the trap weir to the vent connection?

8 feet (Correct answer)
6 feet
4 feet
2 feet

Correct answer: 8 feet

The IPC allows a maximum developed length of 8 feet from the trap weir to the vent for most fixtures.

Question 3: Which of the following fixtures does NOT require a trap under model plumbing codes?

Water closet (Correct answer)
Laundry tub
Shower
Floor drain

Correct answer: Water closet

Water closets have an integral trap built into the bowl and do not require a separate external trap.

Question 4: A laundry chute has gas piping installed.

Must be protected from damage in the normal course of use of the chute
Is required to be installed with only vertical pipe sections
Is a code violation (Correct answer)
Must be secured at maximum intervals of 6 feet

Correct answer: Is a code violation

It is inappropriate to install gas piping in a location that could distribute gas beyond the location of the leak, such as laundry chutes, dumbwaiters, air-circulating ducts, or elevators, which are all prohibited from having gas piping installed in them.

Question 5: A master plumber is sizing a natural gas piping system using the longest length method. The most remote appliance is a furnace located 75 feet from the meter. The total connected load for the entire system is 250,000 BTU/hr. Using a standard sizing table for 0.5 psi gas pressure with a 0.5-inch water column pressure drop, which sizing column should be used to size ALL pipe sections?

The column for the next length longer than 75 feet, such as 80 or 90 feet. (Correct answer)
The column corresponding to the specific length of each individual pipe section.
The column that corresponds to the largest pipe diameter required.
The column for 250 CFH (cubic feet per hour).

Correct answer: The column for the next length longer than 75 feet, such as 80 or 90 feet.

When using the 'longest length method' for gas pipe sizing, the first step is to determine the distance from the point of delivery (meter) to the most remote appliance. This single length is then used to size every section of pipe in the entire system. If the exact length is not listed in the sizing table, the next longer length shown must be used.

Question 6: A plumber is designing a combination waste and vent system for a series of floor drains in a commercial laboratory. Which of the following is a key limitation of this type of system under the IPC?

Vertical risers connecting fixture drains to the horizontal pipe cannot exceed 8 feet. (Correct answer)
The pipe must be sloped at 1/8 inch per foot to ensure proper scouring action.
The maximum developed length of the combination pipe is limited to 50 feet.
Only a maximum of three fixtures can be connected to any single combination waste and vent pipe.

Correct answer: Vertical risers connecting fixture drains to the horizontal pipe cannot exceed 8 feet.

In a combination waste and vent system, the pipe is oversized to allow air to move freely above the waste flow. A critical rule in the IPC is that while the horizontal length of the system is unlimited, any vertical risers from the horizontal pipe up to a fixture drain (like a floor drain) cannot exceed a developed length of 8 feet. If this length is exceeded, the fixture must be vented by other means. The maximum slope is 1/2 inch per foot (4%), not a required 1/8 inch per foot.

Question 7: A plumber is required to have a confined space permit. Which item does NOT need to be on the permit?

The cost estimate for the job (Correct answer)
Names of authorized entrants
Atmospheric test results
Duration of the permit

Correct answer: The cost estimate for the job

OSHA's permit-required confined space standard (29 CFR 1910.146) specifies required permit elements including atmospheric tests, authorized entrants, and duration — but not job cost.

Question 8: According to the NSCP (National Structural Code of the Philippines) and related plumbing standards, what is the minimum water supply fixture unit (WSFU) demand value for a bathtub with a shower combination?

5 WSFU
2 WSFU
3 WSFU
4 WSFU (Correct answer)

Correct answer: 4 WSFU

A bathtub with shower combination is rated at 4 water supply fixture units (WSFU) for supply pipe sizing under Philippine plumbing standards.

Question 9: Which urinal type uses little or no water and relies on a chemical sealant trap to block sewer gases?

Waterless urinal (Correct answer)
Wall-hung washout urinal
Blowout urinal
Siphon-jet urinal

Correct answer: Waterless urinal

Waterless urinals use a floating chemical sealant liquid in the trap that allows urine to pass through but blocks sewer gases from rising.

Question 10: What is the purpose of a dip tube inside a storage-type water heater?

To allow air to escape when the tank is filling
To direct cold incoming water to the bottom of the tank (Correct answer)
To circulate water evenly around the heating element
To drain sediment from the tank bottom during flushing

Correct answer: To direct cold incoming water to the bottom of the tank

The dip tube routes cold supply water to the bottom of the tank, preserving hot water stratification at the top where the outlet is located.

Question 11: Cleanouts must be installed in order to pipe for horizontal drainage branches and building drains. The diameter of the drain and other elements define how far apart these cleanouts should be placed. The drain pipe diameter in this instance is three inches. This drain has a 40-foot running length. The pipe makes one 90-degree turn and one 45-degree turn along this journey. How many cleanouts will this installation require?

6
3
4
2 (Correct answer)

Correct answer: 2

According to the IPC, a cleanout is required for every direction change that is greater than 45 degrees and for every 40 feet of developed length when there are multiple direction changes in a run of pipe. Using these standards, we need one cleanout for a 90 degree turn and one cleanout for every 40 feet of developed length. <br> A cleanout is required by the UPC for every 100 feet of developed pipe length, or any fraction thereof. In addition, a cleanout is required for every aggregate direction change that is greater than 135 degrees. Using these standards, we require 1 cleanout for the distance of 40 feet, which is a fraction of 100 feet, and 1 cleanout for the aggregate direction change because it is greater than 135 degrees.

Question 12: Under the UPC, copper tubing used for water distribution inside a building must be at minimum which type?

Type K
Type DWV
Type L
Type M (Correct answer)

Correct answer: Type M

The UPC allows Type M copper (thinnest wall) for most interior water supply piping in residential applications.

Question 13: A master plumber is installing a sewage ejector pump in a basement sump pit. What is the IPC requirement for venting the sump?

The vent must terminate with an air admittance valve located at least 6 inches above the sump cover.
The vent must be a minimum of 2 inches in diameter, regardless of the pump's discharge rate.
The vent must extend independently to the open air and cannot be connected to other vents.
The vent size is determined by the pump's discharge rating in gallons per minute (GPM) and the developed length. (Correct answer)

Correct answer: The vent size is determined by the pump's discharge rating in gallons per minute (GPM) and the developed length.

The vent for a sewage sump or ejector must be sized based on the pump's discharge capacity (GPM) and the developed length of the vent pipe, as specified in code tables. Air admittance valves are strictly prohibited for this application because they do not relieve positive pressure, allowing sewer gas to escape into the building when the sump fills. The vent must extend to the outdoors.

Question 14: In which of the following scenarios is a Combination Waste and Vent System most likely to be permitted by the authority having jurisdiction?

For venting a battery of water closets in a commercial restroom.
In a new residential kitchen with a sink, dishwasher, and food waste disposer.
To serve as the primary venting method for an entire single-family home.
For floor drains in a large, open-plan grocery store where running conventional vents is structurally impractical. (Correct answer)

Correct answer: For floor drains in a large, open-plan grocery store where running conventional vents is structurally impractical.

Combination waste and vent systems are specialized systems permitted only in limited circumstances, typically where structural conditions make conventional venting impossible or impractical. They are suitable for fixtures like floor drains or sinks in large open areas, like a commercial food preparation area or grocery store, where there are no nearby walls to run vent pipes. They are generally not permitted for fixtures that receive heavy solid waste (like water closets) or suds-producing waste.

Question 15: A master plumber is overseeing the installation of an under-floor cleanout in a crawl space with limited access. According to the Uniform Plumbing Code (UPC), what is the maximum distance the cleanout can be from an access door or crawl hole?

5 feet (Correct answer)
10 feet
15 feet
20 feet

Correct answer: 5 feet

The Uniform Plumbing Code (UPC) specifies that an under-floor cleanout shall not be located more than 5 feet from an access door, trap door, or crawl hole to ensure it is readily accessible for maintenance and rodding.

Question 16: Under the National Building Code of the Philippines (PD 1096) and NPCP, what is the minimum size of the building sewer for a residential structure?

100 mm (4 inches) (Correct answer)
200 mm (8 inches)
150 mm (6 inches)
75 mm (3 inches)

Correct answer: 100 mm (4 inches)

The minimum building sewer size for residential structures is 100 mm (4 inches) per the NPCP and related Philippine building standards.

Question 17: What is the purpose of the 'Hot Work Permit' system on a jobsite where a plumber is soldering near flammable insulation?

To document the plumber's license and insurance
To obtain approval from the local fire marshal before any soldering
To record the type of solder alloy being used
To authorize and control fire-producing activities and establish safeguards (Correct answer)

Correct answer: To authorize and control fire-producing activities and establish safeguards

A Hot Work Permit system is designed to authorize fire-producing work such as soldering or welding and to ensure fire watches, extinguishers, and area clearances are in place.

Question 18: Which of the following connections to a sanitary drainage system is seen to be the most effective?

All of the above
Air gap (Correct answer)
Air break
None of the above

Correct answer: Air gap

An indirect wastepipe is thought to be better protected from back siphonage by an air gap than by an air break. An air break carries a higher risk of a backflow due to the installation process. It is possible for the sanitary drain to become clogged and back up since air breaches have discharge piping entering a receptor. If this happens, contaminated waste may return to the indirect waste fixture. When an air gap is being employed, this is not possible.

Question 19: Under the NPCP, what is the minimum slope (grade) required for a 100 mm (4-inch) horizontal drainage pipe?

1:200 (0.5%)
1:50 (2%)
1:100 (1%) (Correct answer)
1:40 (2.5%)

Correct answer: 1:100 (1%)

The NPCP requires a minimum slope of 1:100 (1% or approximately ¼ inch per foot) for 100 mm horizontal drainage pipes.

Question 20: Which type of respirator is required when working in an atmosphere with an unknown oxygen level in a confined space?

N95 filtering facepiece
Half-face air-purifying respirator
Self-Contained Breathing Apparatus (SCBA) (Correct answer)
Powered Air-Purifying Respirator (PAPR)

Correct answer: Self-Contained Breathing Apparatus (SCBA)

When oxygen levels are unknown or deficient in a confined space, a SCBA must be used because air-purifying respirators do not supply oxygen.

Question 21: Under the National Plumbing Code of the Philippines (NPCP), what is the minimum trap seal depth required for fixture traps?

75 mm (3 inches)
50 mm (2 inches)
38 mm (1.5 inches) (Correct answer)
25 mm (1 inch)

Correct answer: 38 mm (1.5 inches)

The NPCP requires a minimum trap seal depth of 38 mm (1½ inches) to prevent sewer gases from entering the building.

Question 22: What is the standard method used under NPCP to calculate the water demand for a residential building with multiple fixtures?

Manning's equation
Hazen-Williams formula
Hunter's probability method (Hunter's Curve) (Correct answer)
Peak flow rate method

Correct answer: Hunter's probability method (Hunter's Curve)

Hunter's probability method, using Water Supply Fixture Units (WSFU) and Hunter's Curve, is the standard method in the NPCP for estimating peak water demand in buildings.

Question 23: Under the IPC, which backflow prevention device provides the highest level of protection for a high-hazard cross-connection?

Reduced pressure zone (RPZ) assembly (Correct answer)
Double check valve assembly
Pressure vacuum breaker
Atmospheric vacuum breaker

Correct answer: Reduced pressure zone (RPZ) assembly

An RPZ assembly is required for high-hazard connections because it protects against both back-siphonage and back-pressure through a monitored relief port.

Question 24: A sewage ejector pump is required for a basement bathroom group (water closet, lavatory, and shower) that is below the public sewer line. According to common plumbing code standards, what is the minimum size for the sump pit diameter and the discharge pipe for a non-grinder pump serving a water closet?

24-inch diameter pit, 1 1/2-inch discharge
12-inch diameter pit, 1 1/2-inch discharge
18-inch diameter pit, 2-inch discharge (Correct answer)
16-inch diameter pit, 3-inch discharge

Correct answer: 18-inch diameter pit, 2-inch discharge

Most plumbing codes specify a minimum diameter of 18 inches and a minimum depth of 24 or 30 inches for a sewage ejector pit to ensure adequate volume and space for the pump and float controls. For a non-grinder pump that must pass solids from a water closet, the minimum discharge pipe size is typically 2 inches to prevent clogging.

Question 25: According to most model plumbing codes, what is the primary method required to protect the potable water supply at individual shower and tub/shower combination valves against scalding and thermal shock?

Installation of a tempering tank upstream of the water heater.
A mandatory minimum distance of 10 feet between the water heater and the fixture.
Use of oversized PEX tubing to reduce pressure fluctuations.
Installation of individual control valves of the pressure-balance, thermostatic, or combination type. (Correct answer)

Correct answer: Installation of individual control valves of the pressure-balance, thermostatic, or combination type.

Both the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) mandate the use of automatic compensating valves for showers and tub/shower combinations. These can be pressure-balancing, thermostatic, or a combination of both. These devices are designed to automatically adjust to changes in pressure or temperature in the water supply lines, thereby preventing dangerous spikes in outlet temperature that could cause scalding or thermal shock.

Question 26: According to the IPC, what is the minimum diameter for any soil or waste stack that receives the discharge from a water closet?

2 inches
2 1/2 inches
4 inches
3 inches (Correct answer)

Correct answer: 3 inches

To ensure proper transport of solid waste and prevent blockages, model plumbing codes establish a minimum stack size for fixtures discharging significant solids. The International Plumbing Code (IPC) specifies that no water closet shall discharge into a stack less than 3 inches in diameter. While a 4-inch stack is common practice, 3-inch is the minimum code requirement in many residential applications.

Question 27: Which of the following methods can be used to check for leaks in a DWV system?

Smoke
Water
All of the above (Correct answer)
Air

Correct answer: All of the above

Modern DWV systems frequently undergo air testing. The most used testing method in the past was water. Smoke can be utilized to reveal the location of a leak when it is difficult to locate it. Smoke is not the main test technique. The preferred testing medium is air. A minimum of 15 minutes must pass during the testing of a DWV system. Ten pounds per square inch (PSI) must be the minimum test pressure. One riser that is at least ten feet above the main plumbing system is required if just underground plumbing is being checked.

Question 28: A plumber is cutting cast iron pipe with a grinder. What respiratory protection is required for crystalline silica dust exposure?

Full-face SCBA
No protection needed for metal dust
N95 filtering facepiece respirator (Correct answer)
Half-mask with P100 cartridges

Correct answer: N95 filtering facepiece respirator

OSHA's silica standard (29 CFR 1926.1153) requires at minimum an N95 respirator when cutting materials that generate respirable crystalline silica dust.

Question 29: In the NPCP, what is the fixture unit (FU) value assigned to a lavatory (washbasin) for drainage load calculation?

2 FU
3 FU
4 FU
1 FU (Correct answer)

Correct answer: 1 FU

A lavatory is assigned 1 fixture unit for drainage load calculations under the NPCP.

Question 30: A master plumber is reviewing the company's advertising materials, including their website, business cards, and vehicle lettering. According to most state licensing board regulations, which piece of information is almost always required to be included in all forms of advertising?

A list of accepted payment methods.
The company's general liability insurance policy number.
The number of years the business has been in operation.
The master plumber's state-issued license number. (Correct answer)

Correct answer: The master plumber's state-issued license number.

Most state licensing boards for contractors mandate that the official license number be clearly displayed on all advertising, contracts, and business vehicles. This allows consumers to easily verify that the contractor is licensed and in good standing with the state, promoting public safety and accountability.

Question 31: Under OSHA's heat illness prevention guidance, at what heat index level is a jobsite considered to be in the 'High' risk category?

91–103°F (Correct answer)
Above 115°F
80–90°F
103–115°F

Correct answer: 91–103°F

OSHA classifies a heat index of 91–103°F as 'High' risk, requiring additional precautions such as frequent rest breaks, shade, and hydration.

Question 32: A plumbing company's employee, while driving a company-owned van to a job site, negligently runs a red light and causes an accident. Which specific type of business insurance policy would cover the liability for damages to the other vehicle and its occupants?

Workers' Compensation
Commercial General Liability
Inland Marine Insurance
Commercial Auto Insurance (Correct answer)

Correct answer: Commercial Auto Insurance

Commercial Auto Insurance is specifically designed to cover liability and property damage resulting from accidents involving vehicles used for business purposes. Commercial General Liability typically excludes auto accidents, and Workers' Compensation only covers injuries to the company's own employees.

Question 33: In the hierarchy of backflow prevention methods, which of the following is considered the most positive and absolute form of protection?

A Reduced Pressure Zone (RPZ) Assembly
A Pressure Vacuum Breaker (PVB)
An Air Gap (Correct answer)
A Double Check Valve Assembly (DCVA)

Correct answer: An Air Gap

An air gap is the physical, unobstructed vertical separation between the outlet of a potable water supply and the flood-level rim of a receiving vessel. [8, 23] It is the only non-mechanical method and provides the highest possible level of protection because there is no physical path for contaminants to enter the potable water system.

Question 34: Under the OSHA permit-required confined space standard, who is responsible for authorizing entry into a permit space?

The authorized entrant
The attendant
Any licensed contractor on site
The entry supervisor (Correct answer)

Correct answer: The entry supervisor

The entry supervisor is responsible for verifying that conditions are acceptable and authorizing entry into a permit-required confined space.

Question 35: According to the definitions in the International Plumbing Code (IPC), which of the following best describes the 'Building Sewer'?

The lowest horizontal piping of a drainage system inside the building.
The piping that extends from the end of the building drain and conveys its discharge to a public sewer or private disposal system. (Correct answer)
A trap installed in the building drain to prevent the circulation of air from the public sewer.
The main vertical pipe receiving discharge from fixtures on multiple floors.

Correct answer: The piping that extends from the end of the building drain and conveys its discharge to a public sewer or private disposal system.

The IPC specifically defines the 'Building Drain' as the piping inside the building that collects waste and conveys it to a point outside the building wall. The 'Building Sewer' is the pipe that begins where the building drain ends and continues to the public sewer main or other point of disposal.

Question 36: A master plumber is installing a water service for a new single-family residence. The static water pressure from the municipal main is measured at 95 psi. According to the International Plumbing Code (IPC), what is the required action?

Notify the water purveyor to lower the main pressure.
Install a pressure-reducing valve (PRV) set to not exceed 80 psi. (Correct answer)
No action is required as 95 psi is acceptable for residential fixtures.
Install a booster pump to maintain consistent flow.

Correct answer: Install a pressure-reducing valve (PRV) set to not exceed 80 psi.

IPC Section 604.8 requires that a pressure-reducing valve be installed when the static water pressure in the water supply system exceeds 80 psi. This is to protect fixtures, appliances, and piping from damage caused by excessive pressure.

Question 37: What happens if the size of a 4 inch pipe is decreased in the flow's direction?

The waste will travel faster which will allow for better cleaning of the pipe.
This could cause blockage to build up at the reduction point. (Correct answer)
This could cause slugging in the waste system.
This will have no affect on the drainage system.

Correct answer: This could cause blockage to build up at the reduction point.

Due to the flow direction at the reduction point, waste might accumulate and clog the ping system.

Question 38: The IPC requires that vent pipes penetrating a roof extend a minimum of how far above the roof surface in areas subject to frost?

6 inches above the anticipated snow depth
12 inches (Correct answer)
2 inches
6 inches

Correct answer: 12 inches

In frost areas the IPC requires vent terminals to extend at least 12 inches above the roof to prevent frost closure.

Question 39: Which of the following scenarios explicitly requires the installation of a water hammer arrestor according to the IPC?

On any water supply line exceeding 100 feet in developed length.
At the base of every water supply riser in a multi-story building.
On the water supply lines to fixtures with quick-closing valves. (Correct answer)
Immediately downstream of the main water meter for the building.

Correct answer: On the water supply lines to fixtures with quick-closing valves.

The IPC Section 604.9 states that a water hammer arrestor shall be installed where quick-closing valves are used. These valves, such as those on clothes washers and dishwashers, can stop the flow of water abruptly, causing a hydraulic shock (water hammer) that can damage pipes and fixtures. The arrestor absorbs this shock.

Question 40: Which of the following scenarios necessitates the installation of a backflow prevention device or assembly to protect the potable water system?

A gravity-fed water dispenser connected to a bottled water jug.
A standard residential lavatory faucet with an spout ending 8 inches above the flood level rim.
The connection between a water meter and the service line from the public main.
A hose bibb to which a garden hose and chemical sprayer could be attached. (Correct answer)

Correct answer: A hose bibb to which a garden hose and chemical sprayer could be attached.

A hose bibb represents a high-hazard cross-connection because a garden hose can be submerged in a contaminated source (like a puddle, pool, or bucket of cleaning solution) creating a path for back-siphonage. Plumbing codes universally require hose bibbs to be protected by an atmospheric vacuum breaker or other approved backflow prevention device. A standard faucet with a proper air gap does not require an additional device.

Question 41: Who holds the ultimate legal responsibility for ensuring that a required plumbing permit is obtained before work commences on a privately owned property?

The licensed master plumber performing the work.
The property owner. (Correct answer)
The local building department.
The general contractor.

Correct answer: The property owner.

While the licensed plumber typically applies for and obtains the permit on behalf of the owner, model codes place the ultimate responsibility on the owner of the property. It is their legal duty to ensure that any construction or installation on their property complies with all regulations, including securing the necessary permits before work begins.

Question 42: How many P-traps can a single trap arm support in total?

3
1 (Correct answer)
4
2

Correct answer: 1

A trap arm may only have one trap at a time.

Question 43: Using the standard heat formula, approximately how many BTUs are needed to raise 40 gallons of water from 50°F to 120°F?

35,000 BTU
23,300 BTU (Correct answer)
14,000 BTU
18,500 BTU

Correct answer: 23,300 BTU

BTU = gallons × 8.33 lb/gal × ΔT = 40 × 8.33 × 70 ≈ 23,324 BTU.

Question 44: What is the first-hour rating (FHR) of a storage water heater?

The maximum flow rate in GPM at the closest fixture
The gallons of hot water the heater can supply in one hour starting with a full tank (Correct answer)
The time in minutes to fully recover a depleted tank
The recovery rate in BTU per hour at a 90°F temperature rise

Correct answer: The gallons of hot water the heater can supply in one hour starting with a full tank

The FHR measures how many gallons of hot water a heater delivers per hour starting with a full, hot tank — the key metric for sizing to peak demand.

Question 45: A food waste disposer (garbage disposal) installed under a kitchen sink must have its drain connection made to the:

Building drain directly
Downstream side of the P-trap
Tailpiece above the trap inlet (Correct answer)
Dishwasher drain line only

Correct answer: Tailpiece above the trap inlet

The disposer drain must connect to the sink tailpiece above the trap inlet so all waste passes through the trap before entering the drain system.

Question 46: How long can gray water be kept in storage before it can be used to flush a toilet or urinal?

48 hours
96 hours
72 hours (Correct answer)
24 hours

Correct answer: 72 hours

The retention of gray water that will be utilized to flush toilets or urinals may not last longer than 72 hours. Long-term water storage might encourage the growth of microorganisms. The plumbing system does not need this bacteria. For instance, green water in a toilet tank is unattractive and may be dangerous to one's health. The water held in a collection reservoir would be balanced to the fixtures served by a gray water recycling system when it is suitably sized, and the regular daily use of the fixtures will draw down from the reservoir frequently enough to prevent lengthy water storage.

Question 47: Under the Clean Water Act, a plumber who accidentally discharges untreated sewage into a storm drain during a repair must first notify which authority?

The building owner only
The EPA regional office or local environmental agency (Correct answer)
OSHA within 8 hours
The local fire department

Correct answer: The EPA regional office or local environmental agency

Discharges of pollutants including sewage into storm drains or waterways must be reported to the EPA or the relevant state/local environmental agency under the Clean Water Act.

Question 48: Under OSHA's Hazard Communication Standard (HCS), where would a plumber find the most comprehensive information about a chemical sealant's physical and health hazards, first-aid measures, and required personal protective equipment?

The product's warning label on the container.
The Safety Data Sheet (SDS). (Correct answer)
The manufacturer's marketing brochure.
The company's written safety program.

Correct answer: The Safety Data Sheet (SDS).

The Safety Data Sheet (SDS) is a detailed, 16-section document required by OSHA for every hazardous chemical. It contains comprehensive information on properties, hazards, handling precautions, and emergency control measures, which is far more detailed than the container label.

Question 49: In which of the following scenarios is the installation of a trap primer most critical to prevent the release of sewer gas?

A lavatory P-trap in a high-traffic public restroom.
A bathtub drain in a frequently occupied hotel suite.
A kitchen sink in a busy restaurant.
A floor drain located in a seldom-used mechanical room. (Correct answer)

Correct answer: A floor drain located in a seldom-used mechanical room.

Trap primers are devices that add water to a drain trap to maintain its water seal, preventing sewer gas from entering the building. They are most critical for fixtures that are used infrequently, as the water in the trap is subject to evaporation. A floor drain in a mechanical room is a prime example of a location where the trap seal could dry out due to lack of use.

Question 50: Under the OSHA Lockout/Tagout standard, what must be done FIRST before servicing pressurized plumbing systems?

Isolate and de-energize the energy source (Correct answer)
Don PPE appropriate for the pressure level
Notify the building owner
Post a warning sign

Correct answer: Isolate and de-energize the energy source

OSHA's control of hazardous energy standard (29 CFR 1910.147) requires isolation and de-energizing of energy sources before any servicing begins.

Question 51: Under the International Plumbing Code, what is the minimum clearance from the centerline of a water closet to a side wall or obstruction?

18 inches
12 inches
21 inches
15 inches (Correct answer)

Correct answer: 15 inches

The IPC requires a minimum 15-inch clearance from the water closet centerline to any side wall or obstruction.

Question 52: When sizing a hot water recirculation pump, what is the primary engineering factor that determines pump head requirements?

Total storage tank capacity of the water heater
Number and type of plumbing fixtures served
Incoming cold-water supply pressure at the meter
Total pipe length and friction losses in the recirculation loop (Correct answer)

Correct answer: Total pipe length and friction losses in the recirculation loop

Pump head must overcome the total friction losses along the entire recirculation loop length, so pipe length and pipe sizing are the primary inputs for pump selection.

Question 53: A master plumber is designing a natural gas piping system for a commercial building with multiple appliances. The longest pipe run from the meter to the furthest appliance is 150 feet. The total connected load is 450,000 BTU/hr. Using the longest length method and a typical sizing table for 0.5 psi gas pressure with a 0.5-inch water column pressure drop, what is the required pipe size for the main trunk line leaving the meter?

1-inch
2-inch (Correct answer)
1 1/2-inch
1 1/4-inch

Correct answer: 2-inch

Gas pipe sizing tables are based on the length of the longest run, the total BTU/hr load, and the allowable pressure drop. For a 150-foot longest run and a load of 450,000 BTU/hr (or 450 CFH for natural gas), a 1 1/2-inch pipe is typically rated for a lower capacity. Therefore, to safely supply the required volume of gas without excessive pressure drop, the next larger pipe size, which is 2-inch, must be selected. Always consult the specific sizing table in the applicable fuel gas code (like the IFGC).

Question 54: A tankless (on-demand) water heater differs from a storage water heater primarily because it:

Cannot supply multiple fixtures simultaneously
Operates only on natural gas
Heats water only as it flows through the unit with no storage tank (Correct answer)
Requires a larger gas supply line than storage heaters

Correct answer: Heats water only as it flows through the unit with no storage tank

Tankless water heaters heat water on demand as it flows through a heat exchanger, eliminating standby heat loss associated with storage tanks.

Question 55: After completing the installation of a new water service line for a commercial building, what is the generally accepted procedure a master plumber must follow before the system can be put into service, according to most plumbing codes and health standards?

Conduct a hydrostatic pressure test at 150 psi for 4 hours.
Fill the system with a chlorine solution, let it stand, flush, and test for residual chlorine. (Correct answer)
Purge the system with compressed air to remove debris.
Flush the system with hot water for a minimum of 30 minutes.

Correct answer: Fill the system with a chlorine solution, let it stand, flush, and test for residual chlorine.

New potable water systems must be disinfected to kill bacteria introduced during construction. The standard method, outlined in standards like AWWA C651, involves filling the pipes with a chlorine solution (typically 25-50 ppm), allowing it to stand for a specified period (e.g., 24 hours), then flushing with clean water until the chlorine residual is safe.

Question 56: Vacuum pump exhaust must be discharged into the following areas in Med Gas systems:

Designated receptor
Outdoors (Correct answer)
Relief vent
Indirect drain

Correct answer: Outdoors

Exhaust must be sent outside in a manner that reduces the risk of noise and environmental contamination.

Question 57: A plumber is installing a dishwasher in a residence. To prevent the backflow of contaminated water from the sink drain into the dishwasher, which of the following is the most effective and commonly code-required method?

An air gap fitting mounted on the countertop or sink deck. (Correct answer)
Connecting the drain hose to the garbage disposal below the sink's flood level rim.
A check valve installed in the dishwasher's drain line.
A high loop in the drain hose secured to the underside of the countertop.

Correct answer: An air gap fitting mounted on the countertop or sink deck.

An air gap fitting provides a physical separation between the dishwasher drain hose and the drainage system, making it the most reliable method to prevent backflow and cross-contamination. Many plumbing codes specifically mandate an air gap, as it is more effective than a high loop, which can still fail if the drain is completely clogged.

Question 58: Under model plumbing codes, what is the required minimum hot water temperature at the source to prevent Legionella growth?

140°F (Correct answer)
110°F
130°F
120°F

Correct answer: 140°F

Plumbing codes and ASHRAE 188 recommend storing domestic hot water at 140°F to inhibit Legionella bacteria growth.

Question 59: According to the Philippine Sanitation Code, what is the minimum required volume of a septic tank for a residence with 5 persons?

750 liters
1,000 liters (Correct answer)
1,500 liters
2,000 liters

Correct answer: 1,000 liters

PD 856 requires a minimum septic tank volume of 1,000 liters (1 cubic meter) for a household of up to 5 persons.

Question 60: To prevent excessive noise and erosion-corrosion within a copper potable water distribution system, what is the generally recommended maximum design velocity for cold water?

2 feet per second (fps)
4 feet per second (fps)
12 feet per second (fps)
8 feet per second (fps) (Correct answer)

Correct answer: 8 feet per second (fps)

Accepted plumbing engineering practice, as referenced by the Copper Development Association and other industry sources, recommends a maximum velocity of 8 feet per second (fps) for cold water in copper piping. Exceeding this velocity can lead to noise (hydraulic shock) and accelerate the erosion of the pipe's interior surface.

Question 61: A master plumber provides a detailed, written proposal for a bathroom remodel to a homeowner. The proposal includes a scope of work, total price, and payment schedule. The homeowner signs and returns the proposal. Which essential element of a legally binding contract is still missing from this interaction?

Legal Purpose
Acceptance
Consideration (Correct answer)
Offer

Correct answer: Consideration

Consideration is the value that is promised to be exchanged between the parties (e.g., the homeowner's payment and the plumber's work). While the plumber's work is part of the offer, the homeowner has not yet provided their part of the consideration, which is typically an initial payment or deposit. The offer was made by the plumber, and acceptance occurred when the homeowner signed. A bathroom remodel has a legal purpose.

Question 62: A plumber is tasked with installing a roof drain on a flat commercial roof with an unprotected edge 12 feet above the ground. According to OSHA regulations for construction (29 CFR 1926 Subpart M), which of the following is true?

Fall protection is not required if the work is performed more than 10 feet from the edge.
Fall protection is required because the potential fall distance is 6 feet or more. (Correct answer)
A warning line system is the only acceptable form of protection in this scenario.
A trained safety monitor on the roof is sufficient protection by itself.

Correct answer: Fall protection is required because the potential fall distance is 6 feet or more.

OSHA's standard for fall protection in construction, 29 CFR 1926 Subpart M, mandates that fall protection must be provided when workers are on a walking or working surface with an unprotected side or edge that is 6 feet or more above a lower level. The options for protection include guardrail systems, safety net systems, or personal fall arrest systems.

Question 63: When installing a sediment trap for a gas furnace, which of the following configurations is correct according to most fuel gas codes?

A tee fitting with the gas flow entering the top of the tee and exiting the side outlet, with a capped nipple on the bottom. (Correct answer)
A 90-degree elbow with a capped nipple installed on the outlet before the appliance connector.
Installed immediately after the gas meter, before any branches to appliances.
A tee fitting with the gas flow entering one side of the run and exiting the other, with a capped nipple on the bottom.

Correct answer: A tee fitting with the gas flow entering the top of the tee and exiting the side outlet, with a capped nipple on the bottom.

A sediment trap must be configured to change the direction of gas flow, forcing debris to fall out of the gas stream. The correct installation involves a tee fitting where the gas enters the top, makes a 90-degree turn to exit the side outlet towards the appliance, and a capped nipple (minimum 3 inches long) is installed in the bottom opening to collect sediment.

Question 64: A master plumber is working in a city that has adopted a local ordinance requiring a more stringent pipe material for a specific application than what is required by the state's adopted plumbing code. Which requirement must the plumber follow?

The state code, as it has broader jurisdiction.
The less expensive option, as both are technically legal.
The local ordinance, as it is the more restrictive requirement. (Correct answer)
Whichever requirement the project engineer specifies.

Correct answer: The local ordinance, as it is the more restrictive requirement.

A fundamental principle in code administration is that where different codes or regulations have jurisdiction, the most stringent or restrictive requirement shall govern. This ensures the highest level of safety and performance is met. Local amendments are often enacted to address specific local conditions or priorities.

Question 65: Which of the following materials is NOT permitted for gas supply piping under most model plumbing codes?

Schedule 40 black steel pipe
Type K copper
CSST
PVC (Correct answer)

Correct answer: PVC

PVC is not approved for gas supply piping because it is combustible and cannot withstand gas pressure and heat requirements.

Question 66: A horizontal drainage branch connects to the base of a 4-inch drainage stack. According to the IPC, what is the minimum distance downstream from the stack that this horizontal branch connection must be made?

40 inches (Correct answer)
10 inches
8 feet
20 inches

Correct answer: 40 inches

To prevent backflow and interference from the turbulent flow at the base of a stack (an area known as the 'zone of hydraulic jump'), the IPC requires horizontal branches to connect at a minimum distance downstream. This distance is specified as not less than 10 times the diameter of the drainage stack. For a 4-inch stack, this calculates to a minimum of 40 inches (4 inches x 10).

Question 67: Under OSHA 29 CFR 1926, what is the minimum distance that a trench must be from a spoil pile to prevent cave-in hazards?

6 feet
4 feet
2 feet (Correct answer)
8 feet

Correct answer: 2 feet

OSHA requires spoil piles be placed at least 2 feet from the edge of an excavation to prevent material from falling back in and causing a cave-in.

Question 68: According to NFPA 99, medical gas piping must be clearly labeled for safety and identification. Which of the following is a correct labeling requirement?

Painting the entire length of the pipe with the gas-specific color code.
Labeling is only required in patient care areas and mechanical rooms.
Applying labels indicating the gas name and direction of flow at intervals not exceeding 20 feet. (Correct answer)
Using stamped metal tags at every valve and wall penetration only.

Correct answer: Applying labels indicating the gas name and direction of flow at intervals not exceeding 20 feet.

NFPA 99 requires that medical gas and vacuum piping be identified with labels that show the gas name (or symbol) and the direction of flow. These labels must be placed at specific locations, including intervals of no more than 20 feet along the pipe run, at least once in every room, and on both sides of wall penetrations.

Question 69: What is the purpose of a vacuum breaker on a faucet with a threaded hose connection (sillcock)?

To regulate water pressure
To reduce water hammer
To prevent backflow if a hose is submerged in contaminated water (Correct answer)
To limit flow rate

Correct answer: To prevent backflow if a hose is submerged in contaminated water

A hose-connection vacuum breaker prevents back-siphonage in case a garden hose is left submerged in a pool, bucket, or chemical solution.

Question 70: Under federal law, how many days does an employer have to report a work-related hospitalization of an employee to OSHA?

5 days
8 hours
24 hours
3 days (Correct answer)

Correct answer: 3 days

OSHA requires employers to report any work-related in-patient hospitalization within 24 hours, but an in-patient hospitalization of one or more workers must be reported within 24 hours; amputation and eye loss within 24 hours; fatalities within 8 hours.

Question 71: When installing a gas water heater, what is the minimum required clearance between the draft hood diverter and any combustible material?

12 inches
6 inches (Correct answer)
1 inch
2 inches

Correct answer: 6 inches

A minimum 6-inch clearance from combustibles is required around the draft hood diverter due to the heat radiated by exiting flue gases.

Question 72: When soldering copper pipes using a propane torch in a well-ventilated area, what is the MINIMUM personal protective equipment (PPE) required by standard safety practices?

A hard hat and steel-toed boots.
A fire extinguisher and a damp rag.
Safety glasses and heat-resistant gloves. (Correct answer)
A full-face respirator and a leather jacket.

Correct answer: Safety glasses and heat-resistant gloves.

The most immediate and certain hazards during soldering are sparks, flux spatter, and contact with hot pipes and molten solder. Therefore, safety glasses are essential to protect the eyes, and heat-resistant gloves are necessary to protect the hands. While other items contribute to overall safety, eye and hand protection are the minimum direct PPE for the task itself.

Question 73: Under the IPC, what is the maximum number of bathroom groups on the same floor level that can be served by a single horizontal wet vent?

Three
Four
One
Two (Correct answer)

Correct answer: Two

The International Plumbing Code explicitly permits a horizontal wet vent to serve any combination of fixtures within a maximum of two bathroom groups located on the same floor. Each fixture must connect independently to the wet vent.

Question 74: A tankless water heater must deliver 2.5 GPM with a 70°F temperature rise. Approximately how many BTU/hr must it produce?

140,000 BTU/hr
52,500 BTU/hr
105,000 BTU/hr
87,500 BTU/hr (Correct answer)

Correct answer: 87,500 BTU/hr

BTU/hr = GPM × 60 min × 8.33 lb/gal × ΔT = 2.5 × 60 × 8.33 × 70 ≈ 87,465 BTU/hr.

Question 75: A trap seal primer conforming to ASSE 1018 or ASSE 1044 is most commonly required for which of the following fixtures?

A kitchen sink with a garbage disposal.
A residential bathtub that is used daily.
A water closet in a high-traffic public restroom.
An emergency floor drain in a mechanical room. (Correct answer)

Correct answer: An emergency floor drain in a mechanical room.

Trap seal primers are designed to supply water to traps that are used infrequently and are prone to drying out due to evaporation, such as emergency floor drains. This ensures the trap seal is maintained, preventing sewer gas from entering the building.

Question 76: A master plumber is sizing a grease interceptor for a restaurant with two 3-compartment sinks. Which standard governs grease interceptor sizing?

ASSE 1018
ASME A112.14.3
PDI G-101 (Correct answer)
IAPMO PS 23

Correct answer: PDI G-101

PDI G-101 (Plumbing & Drainage Institute) provides the standard sizing method for grease interceptors based on flow rate and retention time.

Question 77: Which ASSE standard governs the performance requirements for pressure-balancing shower valves?

ASSE 1016 (Correct answer)
ASSE 1082
ASSE 1002
ASSE 1070

Correct answer: ASSE 1016

ASSE 1016 covers the performance requirements for automatic compensating shower and tub/shower mixing valves.

Question 78: A backflow event caused by a significant pressure drop in the municipal water main, such as from a main break or firefighting activities, is defined as what condition?

Backsiphonage (Correct answer)
Water hammer
Hydrostatic shock
Backpressure

Correct answer: Backsiphonage

Backsiphonage is the reversal of flow caused by a negative or sub-atmospheric pressure in the supply piping, which can pull contaminants into the potable water system. [1, 5, 7] This is distinct from backpressure, where the downstream system pressure is higher than the supply pressure. [1, 6]

Question 79: A master plumber is required to maintain OSHA 300 logs. After how many on-site employees triggers this recordkeeping requirement?

1 or more
26 or more
11 or more (Correct answer)
5 or more

Correct answer: 11 or more

Employers with 10 or fewer employees are generally exempt from OSHA 300 log recordkeeping; the requirement applies to establishments with 11 or more employees.

Question 80: What type of anode rod is recommended for a water heater connected to a water softener system?

Aluminum-zinc combination anode rod (Correct answer)
Copper anode rod
Titanium anode rod
Magnesium anode rod

Correct answer: Aluminum-zinc combination anode rod

Aluminum-zinc anode rods are preferred for softened water because magnesium rods corrode too rapidly in the elevated-conductivity environment created by salt-based softeners.

Question 81: What is the minimum required slope for a T&P relief valve discharge pipe to ensure complete self-drainage?

1/2 inch per foot
1 inch per foot
1/8 inch per foot
1/4 inch per foot (Correct answer)

Correct answer: 1/4 inch per foot

T&P discharge pipes must slope downward at a minimum 1/4 inch per foot so water drains completely and does not pool in the pipe between relief events.

Master Plumber Exam

The Master Plumber Exam exam validates essential knowledge and skills required for certification or licensure in this field.

Questions

120 min

Time Limit

70%

To Pass

Checking for saved progress...

Exam Rules

You can skip questions and return to them later
Flag questions for review before submitting
No feedback shown until you submit the entire exam
Unanswered questions count as wrong — answer everything
10 pretest questions are mixed in and don't affect your score
Timer auto-submits when time runs out
Your progress is auto-saved every 30 seconds

These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

nyc.gov — Fees, passing score, score release, score validity, exam information · verified Oct 2026
mass.gov — Test delivery, fees, retake policy, score release · verified Oct 2026
tsbpe.texas.gov — Score release, eligibility, fees, renewal, test delivery · verified Oct 2026
michigan.gov — Test delivery · verified Oct 2026
test-takers.psiexams.com — Fees, exam format, passing score, retake policy, time limit, test delivery, exam information · verified Oct 2026
pearsonvue.com — Exam format, passing score, time limit · verified Oct 2026