Master Plumber Exam DWV and Storm Drainage 3 — Questions and Answers
Question 1: What is the purpose of a cleanout in a DWV system?
- To provide access for clearing stoppages (Correct answer)
- To increase the flow velocity
- To reduce pipe size transitions
- To eliminate the need for a vent
Correct answer: To provide access for clearing stoppages
Cleanouts provide access points into drain piping so stoppages can be cleared without dismantling the pipe system.
Question 2: Under the IPC, what is the maximum horizontal distance from a trap to its vent for a 1.5-inch trap arm?
- 3.5 feet
- 5 feet (Correct answer)
- 6 feet
- 8 feet
Correct answer: 5 feet
Per IPC Table 909.1, a 1.5-inch trap arm may not exceed 5 feet from the trap to the vent connection.
Question 3: A relief vent is installed primarily to prevent which condition?
- Pipe freezing
- Pressure buildup in the stack that could unseal traps on lower floors (Correct answer)
- Backflow from the municipal sewer
- Condensation inside vent pipes
Correct answer: Pressure buildup in the stack that could unseal traps on lower floors
A relief vent connects the waste stack to the vent stack to relieve positive pressure that can form at the base of tall stacks and blow trap seals.
Question 4: What is the minimum size of a building sewer serving a single-family residence?
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- 6 inches
Correct answer: 4 inches
The IPC requires a minimum 4-inch building sewer for a single-family dwelling because it serves a water closet.
Question 5: A 'wet vent' serves what dual function?
- It carries both storm water and sanitary waste
- It simultaneously acts as a drain for one fixture and a vent for others (Correct answer)
- It supplies fresh air and removes sewer gases at the same time
- It vents and supplies hot water to fixtures
Correct answer: It simultaneously acts as a drain for one fixture and a vent for others
A wet vent carries the discharge of one fixture while also providing the vent path for other fixtures connected upstream.
Question 6: Which fitting is required when changing direction from vertical to horizontal in a drainage system?
- Standard tee
- Short-sweep 90° elbow
- Long-sweep 90° elbow or combination wye and 1/8 bend (Correct answer)
- Sanitary tee used on its back
Correct answer: Long-sweep 90° elbow or combination wye and 1/8 bend
A long-sweep 90° elbow or combination wye-and-1/8-bend is required for vertical-to-horizontal direction changes to maintain proper flow and prevent blockages.
Question 7: What is 'hydraulic gradient' as it relates to storm drainage design?
- The height of water in a roof drain bowl
- The slope of the energy line representing pressure and elevation head through the pipe (Correct answer)
- The ratio of rainfall intensity to pipe diameter
- The velocity of water at the inlet of a catch basin
Correct answer: The slope of the energy line representing pressure and elevation head through the pipe
Hydraulic gradient represents the slope of the total energy line, used in storm drainage design to ensure pipes flow under gravity without pressurization.
Master Plumber Exam DWV and Storm Drainage 3
What is the purpose of a cleanout in a DWV system?