Master Plumber Exam Drain, Waste, & Vent Systems 4 — Questions and Answers
Question 1: Under the IPC, what is the minimum height above the roof surface for a vent pipe termination in a climate where frost closure is not a concern?
- 4 inches
- 6 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
Vent pipe terminations must extend at least 6 inches above the roof surface, or 12 inches if within 10 feet of a roof-mounted equipment intake.
Question 2: Which condition most commonly causes a trap seal to be lost by evaporation rather than siphoning or back pressure?
- High velocity flow in the drain branch
- A fixture that is seldom used for extended periods (Correct answer)
- Excessive vent pipe diameter
- A drain slope greater than 1/4 inch per foot
Correct answer: A fixture that is seldom used for extended periods
Infrequently used fixtures allow water in the trap to evaporate over time, breaking the seal and allowing sewer gases to enter the building.
Question 3: What is the function of a revent (individual vent or back vent) in a DWV system?
- It vents the building sewer at the property line
- It provides a separate vent connection from a trap back to the vent stack to prevent siphonage (Correct answer)
- It increases the diameter of the main vent stack
- It connects horizontal branch drains to prevent cross-flow
Correct answer: It provides a separate vent connection from a trap back to the vent stack to prevent siphonage
A revent connects the trap arm or drain of a fixture to the vent stack, providing a dedicated air path to prevent trap siphonage caused by negative pressure.
Question 4: According to the IPC, at what interval must cleanouts be installed in a horizontal drain run?
- Every 50 feet
- Every 75 feet
- Every 100 feet (Correct answer)
- Every 150 feet
Correct answer: Every 100 feet
The IPC requires cleanouts to be installed every 100 feet on horizontal drain piping to ensure the entire run can be accessed for clearing.
Question 5: A double sanitary tee (double tee-wye) fitting is used when connecting back-to-back fixtures to permit flow in which directions simultaneously?
- Both upward and downward
- From both sides into a common vertical drop (Correct answer)
- From the top and bottom of a horizontal run
- Into both a vent stack and a drain stack simultaneously
Correct answer: From both sides into a common vertical drop
A double sanitary tee allows simultaneous waste discharge from fixtures on both sides of a wall into a shared vertical drain, each entering the tee from opposite sides.
Question 6: What minimum trap seal depth is required by the IPC for all fixture traps?
- 1 inch
- 2 inches (Correct answer)
- 3 inches
- 4 inches
Correct answer: 2 inches
The IPC mandates a minimum trap seal depth of 2 inches to provide an adequate water barrier against sewer gas entry into occupied spaces.
Question 7: Which venting method allows a vertical drain stack to also serve as its own vent without a separate vent pipe?
- Wet venting
- Air admittance valve venting
- Philadelphia vent (stack venting) (Correct answer)
- Suds relief venting
Correct answer: Philadelphia vent (stack venting)
Philadelphia (stack) venting uses the drainage stack itself as the vent for fixtures connecting directly to it, eliminating separate individual vent pipes under certain conditions.
Master Plumber Exam Drain, Waste, & Vent Systems 4
Under the IPC, what is the minimum height above the roof surface for a vent pipe termination in a climate where frost closure is not a concern?