Master Plumber Licensing Exam Questions
and Correct Answers Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. What is the primary purpose of a plumbing trap?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Improve drainage speed
D. Reduce pipe corrosion
Answer: B. Prevent sewer gases from entering the building
Rationale: A trap holds a water seal that blocks sewer gases from
entering occupied spaces.
2. Which pipe material is commonly used for DWV systems in
residential buildings?
A. Copper Type K
B. PVC
,C. Black steel
D. Galvanized iron
Answer: B. PVC
Rationale: PVC is widely used for drain, waste, and vent systems
because it resists corrosion and is easy to install.
3. What is the minimum slope generally required for horizontal
drainage piping 3 inches and smaller?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1 inch per foot
Answer: C. 1/4 inch per foot
Rationale: Standard plumbing codes typically require a slope of 1/4
inch per foot for proper drainage flow.
4. What device prevents backflow into a potable water system?
A. Pressure switch
B. Vacuum breaker
C. Trap primer
D. Cleanout
,Answer: B. Vacuum breaker
Rationale: Vacuum breakers and other backflow preventers stop
contaminated water from reversing into the potable supply.
5. What is the purpose of a cleanout?
A. Increase venting
B. Access piping for cleaning and maintenance
C. Control water temperature
D. Reduce pressure loss
Answer: B. Access piping for cleaning and maintenance
Rationale: Cleanouts provide access points to remove clogs and
inspect drainage piping.
6. Which fixture requires a vent connection?
A. All plumbing fixtures
B. Only water closets
C. Only sinks
D. Only showers
Answer: A. All plumbing fixtures
Rationale: All trapped fixtures need venting to protect the trap seal
and ensure proper drainage.
7. What is the function of a vent stack?
, A. Carry waste water
B. Supply hot water
C. Equalize air pressure in the drainage system
D. Store water
Answer: C. Equalize air pressure in the drainage system
Rationale: Vent stacks allow air movement, preventing siphonage and
maintaining trap seals.
8. Which tool is commonly used to cut copper tubing?
A. Pipe wrench
B. Tubing cutter
C. Hacksaw blade only
D. Channel locks
Answer: B. Tubing cutter
Rationale: A tubing cutter provides clean, square cuts on copper
tubing.
9. What does DWV stand for?
A. Drain, Waste, and Vent
B. Direct Water Valve
C. Domestic Water Vent
D. Drain Water Volume
and Correct Answers Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a plumbing trap?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Improve drainage speed
D. Reduce pipe corrosion
Answer: B. Prevent sewer gases from entering the building
Rationale: A trap holds a water seal that blocks sewer gases from
entering occupied spaces.
2. Which pipe material is commonly used for DWV systems in
residential buildings?
A. Copper Type K
B. PVC
,C. Black steel
D. Galvanized iron
Answer: B. PVC
Rationale: PVC is widely used for drain, waste, and vent systems
because it resists corrosion and is easy to install.
3. What is the minimum slope generally required for horizontal
drainage piping 3 inches and smaller?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1 inch per foot
Answer: C. 1/4 inch per foot
Rationale: Standard plumbing codes typically require a slope of 1/4
inch per foot for proper drainage flow.
4. What device prevents backflow into a potable water system?
A. Pressure switch
B. Vacuum breaker
C. Trap primer
D. Cleanout
,Answer: B. Vacuum breaker
Rationale: Vacuum breakers and other backflow preventers stop
contaminated water from reversing into the potable supply.
5. What is the purpose of a cleanout?
A. Increase venting
B. Access piping for cleaning and maintenance
C. Control water temperature
D. Reduce pressure loss
Answer: B. Access piping for cleaning and maintenance
Rationale: Cleanouts provide access points to remove clogs and
inspect drainage piping.
6. Which fixture requires a vent connection?
A. All plumbing fixtures
B. Only water closets
C. Only sinks
D. Only showers
Answer: A. All plumbing fixtures
Rationale: All trapped fixtures need venting to protect the trap seal
and ensure proper drainage.
7. What is the function of a vent stack?
, A. Carry waste water
B. Supply hot water
C. Equalize air pressure in the drainage system
D. Store water
Answer: C. Equalize air pressure in the drainage system
Rationale: Vent stacks allow air movement, preventing siphonage and
maintaining trap seals.
8. Which tool is commonly used to cut copper tubing?
A. Pipe wrench
B. Tubing cutter
C. Hacksaw blade only
D. Channel locks
Answer: B. Tubing cutter
Rationale: A tubing cutter provides clean, square cuts on copper
tubing.
9. What does DWV stand for?
A. Drain, Waste, and Vent
B. Direct Water Valve
C. Domestic Water Vent
D. Drain Water Volume
