Plumbing Drainage, Waste & Vent (DWV) 2 — Questions and Answers
Question 1: What is a cleanout and where is it required?
- A water filter installed at the main line
- An access plug that allows clearing of drain line blockages (Correct answer)
- A valve that stops sewer gas
- A device that cleans drinking water
Correct answer: An access plug that allows clearing of drain line blockages
A cleanout is an access plug installed in drain lines that allows a plumber to clear blockages without removing pipe sections, required at direction changes and at specified intervals.
Question 2: What is the purpose of an air admittance valve (AAV)?
- To add air to the water supply for pressure
- To allow air into the drain system without a traditional vent pipe (Correct answer)
- To release excess air from hot water lines
- To prevent backflow in supply lines
Correct answer: To allow air into the drain system without a traditional vent pipe
An AAV (Studor valve) allows air into the drain system to equalize pressure, functioning as a vent without running pipe through the roof.
Question 3: Which fitting should be used when connecting a horizontal drain line to another horizontal drain line at the same elevation?
- Sanitary tee
- 45-degree wye (Correct answer)
- Long-sweep 90
- Street elbow
Correct answer: 45-degree wye
A 45-degree wye fitting is used to connect horizontal drain branches because it promotes laminar flow and reduces the chance of blockages.
Question 4: What is 'hydraulic gradient' in a drain system?
- The velocity of water in supply lines
- The slope maintained in drain pipes to ensure self-cleaning flow (Correct answer)
- The pressure difference between hot and cold water
- The depth of a trap seal
Correct answer: The slope maintained in drain pipes to ensure self-cleaning flow
Hydraulic gradient refers to the slope of drain pipes, which must be maintained at the correct pitch to ensure solids are carried along with water to prevent blockages.
Question 5: What type of vent connects a fixture's drain to a vent stack at a point above the fixture's flood level rim?
- Wet vent
- Island vent
- Individual vent (back vent) (Correct answer)
- Common vent
Correct answer: Individual vent (back vent)
An individual vent, also called a back vent or revent, connects directly from the fixture trap to the vent stack above the fixture's flood level rim.
Question 6: What is the minimum diameter for a building drain that receives discharge from a water closet (toilet)?
- 2 inches
- 3 inches (Correct answer)
- 4 inches
- 6 inches
Correct answer: 3 inches
The IPC requires a minimum 3-inch diameter for any drain pipe that receives waste from a water closet (toilet) to accommodate solid waste.
Plumbing Drainage, Waste & Vent (DWV) 2
What is a cleanout and where is it required?