Exam Questions And Correct Answers

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:

• 1/8 inch per foot
• 1/4 inch per foot
• 3/8 inch per foot
• 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.

• What is the maximum vertical distance between a trap weir and the vent

opening?

• 24 inches
• 6 inches
• 12 inches 1 / 4

• 18 inches

Rationale: The vent opening must be located within 6 inches of the trap

weir to prevent siphonage.

• A cleanout is required for every building drain line at intervals not

exceeding:

• 50 feet
• 75 feet
• 100 feet
• 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:

• 4 inches above the roof
• 6 inches above the roof
• 8 inches above the roof
• 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:

• Twice the diameter of the waste pipe
• Equal to the pipe diameter
• 1 inch minimum
• 1.5 times the pipe diameter 2 / 4

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:

• 2 inches
• 3 inches
• 4 inches
• 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:

• 1–2 inches
• 2–4 inches
• 4–6 inches
• 6–8 inches

Rationale: Trap seals must be deep enough to prevent sewer gas but

shallow enough to avoid siphonage.

• The maximum length of a trap arm (2-inch diameter) without an

additional vent is:

• 3 feet
• 5 feet
• 6 feet
• 8 feet 3 / 4

Rationale: Code limits the trap arm length for 2-inch pipe to 5 feet from

trap weir to vent.

• Which type of fitting should be used to connect a vertical drain to a

horizontal drain?

• Sanitary tee
• Wye or combination wye and 1/8 bend
• Cross fitting
• 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:

• 1/2 inch
• 3/4 inch
• 1 inch
• 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:

• 1.5 inches
• 2.5 inches
• 2 inches
• / 4