Journeyman Plumbers Exam Drainage, Waste, and Vent Systems 4 — Questions and Answers
Question 1: A circuit vent serves:
- A single fixture on an upper floor
- A battery of fixtures connected to a common horizontal branch drain (Correct answer)
- Only floor drains in a single room
- The main soil stack above the roof
Correct answer: A battery of fixtures connected to a common horizontal branch drain
A circuit vent serves a group (battery) of fixtures connected to a horizontal branch drain and provides venting for all fixtures in the group with one vent connection.
Question 2: What is the minimum diameter of a roof vent terminal (vent through roof) under most plumbing codes?
- 1 inch
- 2 inches (Correct answer)
- 3 inches
- 4 inches
Correct answer: 2 inches
The minimum diameter for a vent pipe that terminates through a roof is 2 inches to prevent frost closure in cold climates.
Question 3: When connecting a clothes washer standpipe to the drainage system, the standpipe must extend at least how high above the trap?
- 12 inches
- 18 inches
- 24 inches (Correct answer)
- 36 inches
Correct answer: 24 inches
The IPC requires the clothes washer standpipe to extend at least 18 inches but not more than 42 inches above the trap.
Question 4: An air admittance valve (AAV) is NOT permitted to:
- Serve a single fixture vent on an island sink
- Replace the main vent stack that terminates to open air (Correct answer)
- Vent a lavatory in a remodel where wall access is limited
- Serve a battery of fixtures when permitted by the local code
Correct answer: Replace the main vent stack that terminates to open air
An AAV cannot replace the main vent stack because the drainage system must have at least one open vent pipe to atmosphere to equalize positive pressures.
Question 5: What is the correct location for a cleanout on a building drain near the foundation wall?
- Inside the building, within 10 feet of the foundation
- Outside the building, at the point where the drain exits the foundation (Correct answer)
- At the midpoint of the building drain run
- At the lowest fixture on the lowest floor
Correct answer: Outside the building, at the point where the drain exits the foundation
A cleanout is required near the junction where the building drain exits the foundation so the entire building drain can be rodded from that point.
Question 6: Which statement about common venting is correct?
- Two fixtures on different floors may share a common vent
- Two fixtures on the same floor level with back-to-back traps may share a single common vent (Correct answer)
- A common vent requires a larger diameter than either individual vent
- Common vents are prohibited by the IPC
Correct answer: Two fixtures on the same floor level with back-to-back traps may share a single common vent
A common vent connects two fixture drains at the same level into a single vent pipe, and is permitted when both fixture outlets enter the drain stack or branch at the same level.
Question 7: What is the maximum vertical drop allowed for a trap arm before it connects to the vent?
- There is no vertical drop allowed; trap arms must be horizontal
- One pipe diameter
- The trap arm must slope but cannot drop more than the pipe diameter (Correct answer)
- 6 inches regardless of pipe size
Correct answer: The trap arm must slope but cannot drop more than the pipe diameter
A trap arm must slope toward the drain but cannot drop more than one pipe diameter in total vertical drop before reaching the vent connection.
