Journeyman Plumbers Exam Drainage, Waste, and Vent Systems 3 — Questions and Answers
Question 1: Which of the following fixtures is assigned the highest drainage fixture unit (DFU) value under the IPC?
- Lavatory
- Bathtub
- Water closet (flush tank) (Correct answer)
- Kitchen sink
Correct answer: Water closet (flush tank)
A flush-tank water closet is rated at 3 DFUs, which is higher than a lavatory (1), bathtub (2), or kitchen sink (2).
Question 2: What type of vent is installed downstream of a fixture trap and connects to the vent stack above the fixture's flood level rim?
- Circuit vent
- Individual vent (back vent) (Correct answer)
- Common vent
- Island fixture vent
Correct answer: Individual vent (back vent)
An individual vent (also called a back vent or revent) connects the fixture's trap arm to the vent stack and runs upward past the fixture's flood level rim.
Question 3: An island fixture vent loop is required when:
- A fixture is located more than 6 feet from the main stack
- A sink or similar fixture is installed in an island where a standard vent cannot go up through a wall (Correct answer)
- Any fixture is on the second floor
- The drain slope exceeds 1/2 inch per foot
Correct answer: A sink or similar fixture is installed in an island where a standard vent cannot go up through a wall
Island fixture vent loops route the vent piping under the floor and back up alongside the drain when there is no adjacent wall to run a conventional vent.
Question 4: What is the minimum size of a vent stack serving a soil stack that receives discharge from water closets?
- 1-1/2 inches
- 2 inches
- 3 inches (Correct answer)
- 4 inches
Correct answer: 3 inches
When water closets connect to the soil stack, the vent stack must be at least 3 inches in diameter per IPC sizing requirements.
Question 5: A crown vent is prohibited because:
- It increases sewer gas pressure in the trap
- It is too expensive to install
- Solids can accumulate and block the vent opening at the top of the trap (Correct answer)
- It does not meet the 1/4-inch-per-foot slope requirement
Correct answer: Solids can accumulate and block the vent opening at the top of the trap
A crown vent connects at the crown (top) of the trap, where waste material can collect and plug the vent, rendering it ineffective.
Question 6: Under the IPC, a vent pipe that terminates through an exterior wall must terminate at least how far above the top of the opening it is near?
- 6 inches (Correct answer)
- 12 inches
- 24 inches
- 36 inches
Correct answer: 6 inches
A vent terminating through an exterior wall must end at least 6 inches above the top of any nearby opening such as a window or door.
Question 7: Which of these conditions would cause a trap to lose its water seal due to self-siphonage?
- The vent pipe is too large
- A fixture drain discharges a full slug of water through a long, unvented trap arm (Correct answer)
- The water supply pressure is too high
- The building drain slope is too shallow
Correct answer: A fixture drain discharges a full slug of water through a long, unvented trap arm
Self-siphonage occurs when a full flow of water down an unvented or inadequately vented trap arm creates enough suction to pull the water seal out of the trap.
