PLUMBING CONTRACTOR LICENSING EXAMINER EXAM QUESTIONS AND
ANSWERS (VERIFIED ANSWERS) PLUS RATIONALE 2025/2026 Q&A/
INSTANDOWNLOAD PDF
1. Which of the following materials is most commonly used for water supply pipes in
residential plumbing?
A. PVC
B. Copper
C. Cast iron
D. ABS
Correct answer: B. Copper — Copper pipes are durable, corrosion-resistant, and suitable for
both hot and cold water supply lines.
2. The slope required for horizontal drainage pipes less than 3 inches in diameter is
approximately:
A. 1/4 inch per foot
B. 1/8 inch per foot
C. 1/2 inch per foot
D. 1 inch per foot
Correct answer: A. 1/4 inch per foot — Ensures proper drainage and prevents standing water or
blockages.
3. A plumbing vent primarily serves to:
A. Supply fresh air to fixtures
B. Remove sewer gases and equalize pressure
C. Drain wastewater faster
D. Reduce pipe corrosion
Correct answer: B. Remove sewer gases and equalize pressure — Proper venting prevents trap
siphonage and maintains flow.
4. The trap seal in a plumbing fixture prevents:
A. Water hammer
B. Backflow
C. Sewer gases from entering the building
D. Overpressure
,Correct answer: C. Sewer gases from entering the building — The water seal acts as a barrier
between sewer gases and indoor air.
5. Which test is commonly used to check for leaks in new plumbing systems?
A. Hydrostatic test
B. Air pressure test
C. Both A and B
D. Flow rate test
Correct answer: C. Both A and B — Hydrostatic and air tests are both approved methods
depending on system type.
6. The minimum size of a building drain is usually:
A. 2 inches
B. 3 inches
C. 4 inches
D. 6 inches
Correct answer: C. 4 inches — Standard for residential drains connecting to the building sewer.
7. Backflow prevention devices are installed to:
A. Prevent leaks
B. Maintain water pressure
C. Stop reverse flow of contaminated water
D. Reduce flow rate
Correct answer: C. Stop reverse flow of contaminated water — Ensures potable water is not
polluted by cross-connections.
8. Which of the following is an indirect waste connection?
A. Lavatory drain
B. Dishwasher drain to air gap
C. Bathtub drain
D. Floor drain
Correct answer: B. Dishwasher drain to air gap — Indirect waste uses an air break to prevent
contamination.
9. A cleanout should be installed at every:
A. Change in pipe direction greater than 45°
, B. 10-foot interval
C. Fixture connection
D. Vent termination
Correct answer: A. Change in pipe direction greater than 45° — Allows for easy access for
maintenance and cleaning.
10. The water service pipe connects:
A. Fixtures to traps
B. Traps to drains
C. Street main to building water supply
D. Vent stack to roof
Correct answer: C. Street main to building water supply — It delivers potable water from the
main to the structure.
11. Which of the following valves allows water flow in only one direction?
A. Gate valve
B. Ball valve
C. Check valve
D. Globe valve
Correct answer: C. Check valve — Prevents backflow and maintains system integrity.
12. The plumbing code that governs most U.S. jurisdictions is known as:
A. National Electrical Code (NEC)
B. Uniform Plumbing Code (UPC)
C. Building Safety Code (BSC)
D. International Fire Code (IFC)
Correct answer: B. Uniform Plumbing Code (UPC) — Sets minimum standards for plumbing
design and installation.
13. A vacuum breaker is designed to:
A. Stop leakage
B. Prevent negative pressure and siphonage
C. Reduce water hammer
D. Increase water flow
Correct answer: B. Prevent negative pressure and siphonage — Keeps contaminated water from
being drawn back into the system.
ANSWERS (VERIFIED ANSWERS) PLUS RATIONALE 2025/2026 Q&A/
INSTANDOWNLOAD PDF
1. Which of the following materials is most commonly used for water supply pipes in
residential plumbing?
A. PVC
B. Copper
C. Cast iron
D. ABS
Correct answer: B. Copper — Copper pipes are durable, corrosion-resistant, and suitable for
both hot and cold water supply lines.
2. The slope required for horizontal drainage pipes less than 3 inches in diameter is
approximately:
A. 1/4 inch per foot
B. 1/8 inch per foot
C. 1/2 inch per foot
D. 1 inch per foot
Correct answer: A. 1/4 inch per foot — Ensures proper drainage and prevents standing water or
blockages.
3. A plumbing vent primarily serves to:
A. Supply fresh air to fixtures
B. Remove sewer gases and equalize pressure
C. Drain wastewater faster
D. Reduce pipe corrosion
Correct answer: B. Remove sewer gases and equalize pressure — Proper venting prevents trap
siphonage and maintains flow.
4. The trap seal in a plumbing fixture prevents:
A. Water hammer
B. Backflow
C. Sewer gases from entering the building
D. Overpressure
,Correct answer: C. Sewer gases from entering the building — The water seal acts as a barrier
between sewer gases and indoor air.
5. Which test is commonly used to check for leaks in new plumbing systems?
A. Hydrostatic test
B. Air pressure test
C. Both A and B
D. Flow rate test
Correct answer: C. Both A and B — Hydrostatic and air tests are both approved methods
depending on system type.
6. The minimum size of a building drain is usually:
A. 2 inches
B. 3 inches
C. 4 inches
D. 6 inches
Correct answer: C. 4 inches — Standard for residential drains connecting to the building sewer.
7. Backflow prevention devices are installed to:
A. Prevent leaks
B. Maintain water pressure
C. Stop reverse flow of contaminated water
D. Reduce flow rate
Correct answer: C. Stop reverse flow of contaminated water — Ensures potable water is not
polluted by cross-connections.
8. Which of the following is an indirect waste connection?
A. Lavatory drain
B. Dishwasher drain to air gap
C. Bathtub drain
D. Floor drain
Correct answer: B. Dishwasher drain to air gap — Indirect waste uses an air break to prevent
contamination.
9. A cleanout should be installed at every:
A. Change in pipe direction greater than 45°
, B. 10-foot interval
C. Fixture connection
D. Vent termination
Correct answer: A. Change in pipe direction greater than 45° — Allows for easy access for
maintenance and cleaning.
10. The water service pipe connects:
A. Fixtures to traps
B. Traps to drains
C. Street main to building water supply
D. Vent stack to roof
Correct answer: C. Street main to building water supply — It delivers potable water from the
main to the structure.
11. Which of the following valves allows water flow in only one direction?
A. Gate valve
B. Ball valve
C. Check valve
D. Globe valve
Correct answer: C. Check valve — Prevents backflow and maintains system integrity.
12. The plumbing code that governs most U.S. jurisdictions is known as:
A. National Electrical Code (NEC)
B. Uniform Plumbing Code (UPC)
C. Building Safety Code (BSC)
D. International Fire Code (IFC)
Correct answer: B. Uniform Plumbing Code (UPC) — Sets minimum standards for plumbing
design and installation.
13. A vacuum breaker is designed to:
A. Stop leakage
B. Prevent negative pressure and siphonage
C. Reduce water hammer
D. Increase water flow
Correct answer: B. Prevent negative pressure and siphonage — Keeps contaminated water from
being drawn back into the system.
