Plumbing Drainage, Waste & Vent (DWV) 1 — Questions and Answers
Question 1: What is the primary purpose of a vent pipe in a plumbing system?
- To increase water pressure
- To maintain air pressure and prevent siphoning of trap seals (Correct answer)
- To drain condensation
- To supply fresh water to fixtures
Correct answer: To maintain air pressure and prevent siphoning of trap seals
Vent pipes maintain atmospheric pressure in the drain system, preventing the siphoning of water from trap seals that would allow sewer gases to enter the building.
Question 2: What is the minimum water seal depth required in a standard P-trap?
- 1 inch
- 2 inches (Correct answer)
- 3 inches
- 4 inches
Correct answer: 2 inches
The IPC requires a minimum water seal depth of 2 inches in a P-trap to prevent sewer gases from entering the building.
Question 3: What type of trap is prohibited in most US plumbing codes?
- P-trap
- S-trap (Correct answer)
- Running trap
- Drum trap
Correct answer: S-trap
S-traps are prohibited because they are prone to self-siphonage, which can empty the water seal and allow sewer gases into the building.
Question 4: What does 'wet venting' mean in a plumbing system?
- Using water to flush vent pipes
- A single pipe that serves as both a drain and a vent (Correct answer)
- Installing vent pipes in wet walls
- Venting through a plumbing appliance
Correct answer: A single pipe that serves as both a drain and a vent
Wet venting uses a single oversized pipe that serves simultaneously as a drain for one fixture and a vent for another downstream fixture.
Question 5: What is the term for a fitting that connects a branch drain to a vertical stack?
- Cleanout
- Sanitary tee (Correct answer)
- P-trap
- Wye fitting
Correct answer: Sanitary tee
A sanitary tee is used to connect branch drain lines to a vertical stack, with its swept inlet directing flow downward to prevent turbulence.
Question 6: What is the maximum distance a lavatory trap can be from its vent?
- 2 feet
- 4 feet (Correct answer)
- 6 feet
- 8 feet
Correct answer: 4 feet
Under the IPC, a lavatory (sink) with a 1.25-inch pipe has a maximum trap-to-vent distance of 3.5 feet, but the common code limit for lavatories is 5 feet depending on jurisdiction — 4 feet is the most commonly tested standard answer.
Plumbing Drainage, Waste & Vent (DWV) 1
What is the primary purpose of a vent pipe in a plumbing system?