Master Plumber Licensing Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The minimum size of a building drain shall not be less than
A. 2 inches
B. 3 inches
C. 4 inches
D. 1½ inches
Rationale: The code requires a minimum 3-inch drain for a single-
family dwelling to handle combined discharge loads.
2. A vent pipe must be installed to prevent
A. Water pressure loss
B. Air infiltration
C. Trap seal siphonage
D. Pipe corrosion
, Rationale: Vents allow air into the drainage system to prevent
siphonage and maintain trap seals.
3. The minimum slope for a 4-inch horizontal drainage pipe is
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 1/2 inch per foot
D. Level
Rationale: A 1/4 inch per foot slope ensures proper flow and prevents
solids from settling.
4. The main vent stack shall 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. 10 inches above the roof
Rationale: Minimum extension above the roof prevents snow or
debris from blocking the vent.
5. The maximum distance between a trap and its vent for a 2-inch trap
arm is
A. 2 feet
B. 3 feet
C. 5 feet
D. 8 feet
, Rationale: Trap arm length is limited by pipe diameter to prevent
siphonage due to pressure drop.
6. The water service pipe must be buried not less than
A. 12 inches below frost line
B. 6 inches below grade
C. 8 inches below grade
D. 10 inches below grade
Rationale: Burial below frost line prevents freezing and pipe rupture.
7. The minimum trap seal depth is
A. 1 inch
B. 1½ inches
C. 2 inches
D. 3 inches
Rationale: A 2-inch trap seal prevents sewer gases from entering the
building.
8. The minimum size of a water closet branch drain is
A. 2 inches
B. 2½ inches
C. 3 inches
D. 4 inches
Rationale: Water closets require a 3-inch drain to handle discharge
volume.
, 9. The proper method to test a water supply system is
A. Smoke test
B. Hydrostatic pressure test
C. Air test
D. Flow test
Rationale: Hydrostatic testing ensures water-tightness under
operational pressure.
10. Backflow prevention is required to prevent
A. Air infiltration
B. Contamination of potable water
C. Pressure surges
D. Leakage
Rationale: Backflow devices stop contaminated water from entering
the potable system.
11. The minimum vertical distance between a water supply outlet
and the flood level rim is
A. 1 inch
B. 2 inches
C. 1 inch above flood level rim
D. 3 inches
Rationale: Air gaps prevent cross-connection and back-siphonage.
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The minimum size of a building drain shall not be less than
A. 2 inches
B. 3 inches
C. 4 inches
D. 1½ inches
Rationale: The code requires a minimum 3-inch drain for a single-
family dwelling to handle combined discharge loads.
2. A vent pipe must be installed to prevent
A. Water pressure loss
B. Air infiltration
C. Trap seal siphonage
D. Pipe corrosion
, Rationale: Vents allow air into the drainage system to prevent
siphonage and maintain trap seals.
3. The minimum slope for a 4-inch horizontal drainage pipe is
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 1/2 inch per foot
D. Level
Rationale: A 1/4 inch per foot slope ensures proper flow and prevents
solids from settling.
4. The main vent stack shall 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. 10 inches above the roof
Rationale: Minimum extension above the roof prevents snow or
debris from blocking the vent.
5. The maximum distance between a trap and its vent for a 2-inch trap
arm is
A. 2 feet
B. 3 feet
C. 5 feet
D. 8 feet
, Rationale: Trap arm length is limited by pipe diameter to prevent
siphonage due to pressure drop.
6. The water service pipe must be buried not less than
A. 12 inches below frost line
B. 6 inches below grade
C. 8 inches below grade
D. 10 inches below grade
Rationale: Burial below frost line prevents freezing and pipe rupture.
7. The minimum trap seal depth is
A. 1 inch
B. 1½ inches
C. 2 inches
D. 3 inches
Rationale: A 2-inch trap seal prevents sewer gases from entering the
building.
8. The minimum size of a water closet branch drain is
A. 2 inches
B. 2½ inches
C. 3 inches
D. 4 inches
Rationale: Water closets require a 3-inch drain to handle discharge
volume.
, 9. The proper method to test a water supply system is
A. Smoke test
B. Hydrostatic pressure test
C. Air test
D. Flow test
Rationale: Hydrostatic testing ensures water-tightness under
operational pressure.
10. Backflow prevention is required to prevent
A. Air infiltration
B. Contamination of potable water
C. Pressure surges
D. Leakage
Rationale: Backflow devices stop contaminated water from entering
the potable system.
11. The minimum vertical distance between a water supply outlet
and the flood level rim is
A. 1 inch
B. 2 inches
C. 1 inch above flood level rim
D. 3 inches
Rationale: Air gaps prevent cross-connection and back-siphonage.
