Master Plumber Licensing Exam Questions
With Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. Which material is most commonly used for residential water
supply piping?
A. Cast iron
B. Copper
C. Galvanized steel
D. Lead
Copper is widely used due to its durability, resistance to
corrosion, and ease of installation, making it standard in modern
residential plumbing.
2. What is the purpose of a backflow preventer in a plumbing
system?
A. To increase water pressure
B. To regulate water temperature
C. To prevent contaminated water from flowing back into the
potable supply
D. To reduce water usage
, A backflow preventer protects drinking water by stopping
reverse flow, which could allow contaminants to enter the
potable water system.
3. What is the minimum slope for a 2-inch horizontal drain pipe
according to most plumbing codes?
A. 1/16 inch per foot
B. 1/32 inch per foot
C. 1/2 inch per foot
D. 1/4 inch per foot
Drainage pipes must be sloped properly to ensure gravity carries
waste and prevents standing water.
4. Which type of valve is best for completely shutting off water flow?
A. Gate valve
B. Ball valve
C. Globe valve
D. All of the above
Gate, ball, and globe valves can each fully stop water flow, but
selection often depends on specific system requirements.
5. When soldering copper pipes, which of the following is critical to
prevent leaks?
A. Use only lead solder
, B. Clean and flux the joint properly
C. Heat the pipe excessively
D. Apply solder before heating
Proper cleaning and flux application ensure a strong bond and
leak-free joint.
6. Which pipe material is typically used for underground potable
water supply?
A. PVC
B. CPVC
C. PEX
D. Galvanized steel
PEX is durable, flexible, and resistant to corrosion, making it
suitable for underground water lines.
7. A vent stack in a plumbing system primarily prevents:
A. Low water pressure
B. Traps from being siphoned
C. Overflow from toilets
D. Pipe corrosion
Vent stacks allow air into the system, maintaining proper
pressure to prevent water in traps from being siphoned out.
, 8. How often should a water heater’s pressure relief valve be tested?
A. Never
B. Every 5 years
C. Annually
D. Every month
Annual testing ensures that the valve operates correctly and
prevents dangerous pressure buildup.
9. What is the primary purpose of a P-trap?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Filter debris
D. Reduce water usage
The P-trap retains a small amount of water to block sewer gases
while allowing wastewater to flow.
10. When installing a shower valve, what must be considered for
code compliance?
A. Pipe material only
B. Distance from finished floor to valve handle
C. Water pressure only
D. Trap type
With Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. Which material is most commonly used for residential water
supply piping?
A. Cast iron
B. Copper
C. Galvanized steel
D. Lead
Copper is widely used due to its durability, resistance to
corrosion, and ease of installation, making it standard in modern
residential plumbing.
2. What is the purpose of a backflow preventer in a plumbing
system?
A. To increase water pressure
B. To regulate water temperature
C. To prevent contaminated water from flowing back into the
potable supply
D. To reduce water usage
, A backflow preventer protects drinking water by stopping
reverse flow, which could allow contaminants to enter the
potable water system.
3. What is the minimum slope for a 2-inch horizontal drain pipe
according to most plumbing codes?
A. 1/16 inch per foot
B. 1/32 inch per foot
C. 1/2 inch per foot
D. 1/4 inch per foot
Drainage pipes must be sloped properly to ensure gravity carries
waste and prevents standing water.
4. Which type of valve is best for completely shutting off water flow?
A. Gate valve
B. Ball valve
C. Globe valve
D. All of the above
Gate, ball, and globe valves can each fully stop water flow, but
selection often depends on specific system requirements.
5. When soldering copper pipes, which of the following is critical to
prevent leaks?
A. Use only lead solder
, B. Clean and flux the joint properly
C. Heat the pipe excessively
D. Apply solder before heating
Proper cleaning and flux application ensure a strong bond and
leak-free joint.
6. Which pipe material is typically used for underground potable
water supply?
A. PVC
B. CPVC
C. PEX
D. Galvanized steel
PEX is durable, flexible, and resistant to corrosion, making it
suitable for underground water lines.
7. A vent stack in a plumbing system primarily prevents:
A. Low water pressure
B. Traps from being siphoned
C. Overflow from toilets
D. Pipe corrosion
Vent stacks allow air into the system, maintaining proper
pressure to prevent water in traps from being siphoned out.
, 8. How often should a water heater’s pressure relief valve be tested?
A. Never
B. Every 5 years
C. Annually
D. Every month
Annual testing ensures that the valve operates correctly and
prevents dangerous pressure buildup.
9. What is the primary purpose of a P-trap?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Filter debris
D. Reduce water usage
The P-trap retains a small amount of water to block sewer gases
while allowing wastewater to flow.
10. When installing a shower valve, what must be considered for
code compliance?
A. Pipe material only
B. Distance from finished floor to valve handle
C. Water pressure only
D. Trap type
