Master Plumber Exam Drain, Waste, & Vent Systems 3 — Questions and Answers
Question 1: Which material is NOT permitted for underground drain piping inside a building per the IPC?
- ABS (acrylonitrile butadiene styrene)
- Cast iron
- PVC (polyvinyl chloride)
- Galvanized steel (Correct answer)
Correct answer: Galvanized steel
Galvanized steel is not listed by the IPC as an approved material for underground drain, waste, and vent piping due to corrosion susceptibility.
Question 2: What is the maximum number of fixture units that can drain into a 4-inch horizontal branch drain?
- 160 fixture units
- 216 fixture units (Correct answer)
- 256 fixture units
- 300 fixture units
Correct answer: 216 fixture units
Per IPC drainage fixture unit tables, a 4-inch horizontal branch drain can handle a maximum of 216 fixture units.
Question 3: An air admittance valve (AAV) may NOT be used as the sole vent for which application under the IPC?
- A single lavatory
- A kitchen sink
- The main stack vent termination to outside air (Correct answer)
- An island fixture
Correct answer: The main stack vent termination to outside air
At least one vent in every building must extend to open outdoor air; an AAV cannot replace the required outdoor vent termination for the entire building's DWV system.
Question 4: What is the minimum diameter for a building sewer serving a single-family home with up to 21 drainage fixture units?
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- 6 inches
Correct answer: 4 inches
The IPC requires a minimum 4-inch building sewer for a single-family dwelling regardless of the calculated fixture unit load.
Question 5: A sanitary tee fitting may be used in which orientation for drain connections?
- On its back (horizontal to horizontal)
- Upright with flow entering from the side branch vertically downward (Correct answer)
- Inverted (horizontal flow entering from the top)
- As a horizontal to horizontal change of direction only
Correct answer: Upright with flow entering from the side branch vertically downward
A sanitary tee is approved only in the upright position where the branch enters from the side and flow descends into the vertical leg, not laid on its back for horizontal connections.
Question 6: When a drain pipe transitions from vertical to horizontal, which fitting provides the most hydraulically efficient change of direction?
- 1/4 bend (90° elbow)
- 1/8 bend (45° elbow)
- Long-sweep 1/4 bend (Correct answer)
- Short-pattern tee-wye
Correct answer: Long-sweep 1/4 bend
A long-sweep 1/4 bend provides the gentlest transition from vertical to horizontal flow, minimizing turbulence and the risk of blockage.
Question 7: What is the term for a vent that connects multiple trap arms to a single common vent pipe in a battery of fixtures?
- Individual vent
- Circuit vent (Correct answer)
- Common vent
- Continuous vent
Correct answer: Circuit vent
A circuit vent connects the trap arms of a series of fixtures on a horizontal branch to a single vent riser, commonly used for back-to-back fixtures or fixture batteries.
Master Plumber Exam Drain, Waste, & Vent Systems 3
Which material is NOT permitted for underground drain piping inside a building per the IPC?