Master Plumber Licensing Exam

Master Plumber Licensing Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The minimum size of a building drain shall not be less than
• 2 inches
• 3 inches
• 4 inches
• 1½ inches

Rationale: The code requires a minimum 3-inch drain for a single-

family dwelling to handle combined discharge loads.

• A vent pipe must be installed to prevent
• Water pressure loss
• Air infiltration
• Trap seal siphonage
• Pipe corrosion 1 / 4

Rationale: Vents allow air into the drainage system to prevent

siphonage and maintain trap seals.

• The minimum slope for a 4-inch horizontal drainage pipe is
• 1/8 inch per foot
• 1/4 inch per foot
• 1/2 inch per foot
• Level

Rationale: A 1/4 inch per foot slope ensures proper flow and prevents

solids from settling.

• The main vent stack shall extend through the roof not less than
• 4 inches above the roof
• 6 inches above the roof
• 8 inches above the roof
• 10 inches above the roof

Rationale: Minimum extension above the roof prevents snow or

debris from blocking the vent.

• The maximum distance between a trap and its vent for a 2-inch trap

arm is

• 2 feet
• 3 feet
• 5 feet
• 8 feet 2 / 4

Rationale: Trap arm length is limited by pipe diameter to prevent

siphonage due to pressure drop.

• The water service pipe must be buried not less than
• 12 inches below frost line
• 6 inches below grade
• 8 inches below grade
• 10 inches below grade

Rationale: Burial below frost line prevents freezing and pipe rupture.

• The minimum trap seal depth is
• 1 inch
• 1½ inches
• 2 inches
• 3 inches

Rationale: A 2-inch trap seal prevents sewer gases from entering the

building.

• The minimum size of a water closet branch drain is
• 2 inches
• 2½ inches
• 3 inches
• 4 inches

Rationale: Water closets require a 3-inch drain to handle discharge

volume. 3 / 4

• The proper method to test a water supply system is
• Smoke test
• Hydrostatic pressure test
• Air test
• Flow test

Rationale: Hydrostatic testing ensures water-tightness under

operational pressure.

• Backflow prevention is required to prevent
• Air infiltration
• Contamination of potable water
• Pressure surges
• Leakage

Rationale: Backflow devices stop contaminated water from entering

the potable system.

• The minimum vertical distance between a water supply outlet

and the flood level rim is

• 1 inch
• 2 inches
• 1 inch above flood level rim
• 3 inches

Rationale: Air gaps prevent cross-connection and back-siphonage.

• / 4