Master Plumber Licensing Practice
Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The minimum slope for a 3-inch horizontal drainage pipe is:
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 3/8 inch per foot
D. 1/2 inch per foot
Rationale: The Uniform Plumbing Code requires a minimum slope of 1/4
inch per foot for 2½-inch to 3-inch pipes to ensure proper flow velocity.
2. What is the maximum vertical distance between a trap weir and the vent
opening?
A. 24 inches
B. 6 inches
C. 12 inches
,D. 18 inches
Rationale: The vent opening must be located within 6 inches of the trap
weir to prevent siphonage.
3. A cleanout is required for every building drain line at intervals not
exceeding:
A. 50 feet
B. 75 feet
C. 100 feet
D. 150 feet
Rationale: Code requires cleanouts at not more than 100 feet apart for
horizontal drainage lines.
4. The main vent stack should extend through the roof not less than:
A. 4 inches above the roof
B. 6 inches above the roof
C. 8 inches above the roof
D. 12 inches above the roof
Rationale: Minimum extension above the roof is 6 inches to prevent
obstruction from snow or debris.
5. The air gap for an indirect waste pipe shall be at least:
A. Twice the diameter of the waste pipe
B. Equal to the pipe diameter
C. 1 inch minimum
D. 1.5 times the pipe diameter
,Rationale: Code mandates an air gap twice the diameter of the outlet to
prevent backflow.
6. The minimum size of a building sewer serving one water closet is:
A. 2 inches
B. 3 inches
C. 4 inches
D. 5 inches
Rationale: A 4-inch sewer line is the minimum allowed for a system with at
least one toilet.
7. The trap seal depth must be between:
A. 1–2 inches
B. 2–4 inches
C. 4–6 inches
D. 6–8 inches
Rationale: Trap seals must be deep enough to prevent sewer gas but
shallow enough to avoid siphonage.
8. The maximum length of a trap arm (2-inch diameter) without an
additional vent is:
A. 3 feet
B. 5 feet
C. 6 feet
D. 8 feet
, Rationale: Code limits the trap arm length for 2-inch pipe to 5 feet from
trap weir to vent.
9. Which type of fitting should be used to connect a vertical drain to a
horizontal drain?
A. Sanitary tee
B. Wye or combination wye and 1/8 bend
C. Cross fitting
D. Street elbow
Rationale: Wye-type fittings promote smooth flow transition from vertical
to horizontal.
10. The minimum water service pipe size for a single-family dwelling is:
A. 1/2 inch
B. 3/4 inch
C. 1 inch
D. 5/8 inch
Rationale: A 3/4-inch service line ensures adequate flow and pressure for
domestic use.
11. The minimum vent pipe size for a water closet is:
A. 1.5 inches
B. 2.5 inches
C. 2 inches
Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The minimum slope for a 3-inch horizontal drainage pipe is:
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 3/8 inch per foot
D. 1/2 inch per foot
Rationale: The Uniform Plumbing Code requires a minimum slope of 1/4
inch per foot for 2½-inch to 3-inch pipes to ensure proper flow velocity.
2. What is the maximum vertical distance between a trap weir and the vent
opening?
A. 24 inches
B. 6 inches
C. 12 inches
,D. 18 inches
Rationale: The vent opening must be located within 6 inches of the trap
weir to prevent siphonage.
3. A cleanout is required for every building drain line at intervals not
exceeding:
A. 50 feet
B. 75 feet
C. 100 feet
D. 150 feet
Rationale: Code requires cleanouts at not more than 100 feet apart for
horizontal drainage lines.
4. The main vent stack should extend through the roof not less than:
A. 4 inches above the roof
B. 6 inches above the roof
C. 8 inches above the roof
D. 12 inches above the roof
Rationale: Minimum extension above the roof is 6 inches to prevent
obstruction from snow or debris.
5. The air gap for an indirect waste pipe shall be at least:
A. Twice the diameter of the waste pipe
B. Equal to the pipe diameter
C. 1 inch minimum
D. 1.5 times the pipe diameter
,Rationale: Code mandates an air gap twice the diameter of the outlet to
prevent backflow.
6. The minimum size of a building sewer serving one water closet is:
A. 2 inches
B. 3 inches
C. 4 inches
D. 5 inches
Rationale: A 4-inch sewer line is the minimum allowed for a system with at
least one toilet.
7. The trap seal depth must be between:
A. 1–2 inches
B. 2–4 inches
C. 4–6 inches
D. 6–8 inches
Rationale: Trap seals must be deep enough to prevent sewer gas but
shallow enough to avoid siphonage.
8. The maximum length of a trap arm (2-inch diameter) without an
additional vent is:
A. 3 feet
B. 5 feet
C. 6 feet
D. 8 feet
, Rationale: Code limits the trap arm length for 2-inch pipe to 5 feet from
trap weir to vent.
9. Which type of fitting should be used to connect a vertical drain to a
horizontal drain?
A. Sanitary tee
B. Wye or combination wye and 1/8 bend
C. Cross fitting
D. Street elbow
Rationale: Wye-type fittings promote smooth flow transition from vertical
to horizontal.
10. The minimum water service pipe size for a single-family dwelling is:
A. 1/2 inch
B. 3/4 inch
C. 1 inch
D. 5/8 inch
Rationale: A 3/4-inch service line ensures adequate flow and pressure for
domestic use.
11. The minimum vent pipe size for a water closet is:
A. 1.5 inches
B. 2.5 inches
C. 2 inches
