Master Plumber Exam Drainage, Waste, and Venting 4 — Questions and Answers
Question 1: What is the minimum trap seal depth required by the IPC for fixture traps?
- 1 inch
- 2 inches (Correct answer)
- 3 inches
- 4 inches
Correct answer: 2 inches
The IPC requires a minimum trap seal depth of 2 inches to prevent sewer gases from entering the building through the fixture drain.
Question 2: A stack vent differs from a vent stack in that a stack vent:
- Serves only one fixture
- Is an extension of the drain stack above the highest branch connection (Correct answer)
- Connects the drain stack to the vent stack
- Is installed only in one-story buildings
Correct answer: Is an extension of the drain stack above the highest branch connection
A stack vent is the upper portion of the soil or waste stack that extends above the highest horizontal branch and serves as the vent terminal.
Question 3: What is the term for the pressure condition created by rapid water flow past a branch connection that can siphon a trap?
- Back-pressure siphonage
- Induced siphonage (Correct answer)
- Self-siphonage
- Momentum siphonage
Correct answer: Induced siphonage
Induced siphonage occurs when waste flowing down a stack creates negative pressure at a nearby branch connection, pulling water out of adjacent fixture traps.
Question 4: Under the IPC, what is the maximum height of a horizontal offset in a drainage stack that requires a relief vent?
- More than 3 stories above the offset
- More than 5 stories above the offset (Correct answer)
- More than 8 stories above the offset
- A relief vent is always required at any offset
Correct answer: More than 5 stories above the offset
The IPC requires a relief vent when a horizontal offset in a drainage stack has more than 5 stories of drainage stack above it.
Question 5: A grease interceptor is required to have a vented inlet. What is the reason for this requirement?
- To prevent the interceptor from overflowing
- To prevent siphoning of the trap seal and allow gas escape (Correct answer)
- To provide oxygen for grease-digesting bacteria
- To equalize pressure with the building sewer
Correct answer: To prevent siphoning of the trap seal and allow gas escape
Venting the inlet of a grease interceptor prevents the trap seal from being siphoned and allows gases produced by decomposing grease to escape safely.
Question 6: What is the minimum size of a cleanout required on a building drain 4 inches in diameter?
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- Full-size only
Correct answer: 4 inches
The IPC requires that a cleanout on a pipe 4 inches or less in diameter must be the same size as the pipe, so a 4-inch drain requires a 4-inch cleanout.
Question 7: Island fixture venting is a special venting method most commonly used for:
- Toilets installed in bathroom pods
- Sinks installed in kitchen islands away from walls (Correct answer)
- Urinals in gang restrooms
- Floor drains in mechanical rooms
Correct answer: Sinks installed in kitchen islands away from walls
Island venting routes the vent pipe down below the floor and back up to connect to the vent system, allowing sinks in islands without wall access to be properly vented.
Master Plumber Exam Drainage, Waste, and Venting 4
What is the minimum trap seal depth required by the IPC for fixture traps?