Master Plumber Licensing Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A
1. The minimum slope required for a 3-inch horizontal drain pipe is:
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Proper slope ensures gravity drainage and prevents standing
water in the pipe.
2. Which type of valve is typically used to control water flow in a
domestic hot water system?
A. Gate valve
B. Check valve
C. Ball valve
D. Butterfly valve
Ball valves provide reliable shutoff and are easy to operate.
3. What is the primary purpose of a plumbing vent?
A. Reduce water pressure
B. Filter debris
C. Allow air into the drainage system to prevent siphoning of
traps
, D. Heat water in the system
Vents maintain proper pressure in drainage lines, preventing traps
from being emptied.
4. A backflow preventer is required when:
A. Connecting a water heater
B. There is a potential for cross-connection with contaminated
water
C. Installing a new faucet
D. Replacing a drain pipe
This prevents contamination of the potable water supply.
5. What is the typical maximum spacing for supports on a 2-inch PVC
drain line?
A. 2 feet
B. 3 feet
C. 4 feet
D. 6 feet
Proper support prevents sagging and ensures proper drainage.
6. The term "DWV" in plumbing stands for:
A. Direct Water Valve
B. Domestic Water Vent
C. Drain, Waste, and Vent
D. Dual Water Valve
DWV systems manage all non-pressurized plumbing flows in a
building.
7. Which material is most commonly used for underground water
supply lines?
A. Copper
, B. PEX
C. Cast iron
D. Galvanized steel
PEX is flexible, resistant to corrosion, and easy to install
underground.
8. Which fixture requires a trap?
A. Water heater
B. Sink
C. Water meter
D. Boiler
Traps prevent sewer gases from entering living spaces.
9. What is the purpose of a pressure-reducing valve?
A. Increase flow
B. Lower incoming water pressure to safe levels
C. Divert water
D. Measure water usage
High pressure can damage plumbing fixtures and appliances.
10. The maximum distance a water closet trap arm can extend
without venting is:
A. 12 inches
B. 24 inches
C. 30 inches
D. 36 inches
Venting prevents siphoning and ensures proper trap function.
11. What is the standard water supply pipe size for a residential
kitchen sink?
A. 1/2 inch
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A
1. The minimum slope required for a 3-inch horizontal drain pipe is:
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Proper slope ensures gravity drainage and prevents standing
water in the pipe.
2. Which type of valve is typically used to control water flow in a
domestic hot water system?
A. Gate valve
B. Check valve
C. Ball valve
D. Butterfly valve
Ball valves provide reliable shutoff and are easy to operate.
3. What is the primary purpose of a plumbing vent?
A. Reduce water pressure
B. Filter debris
C. Allow air into the drainage system to prevent siphoning of
traps
, D. Heat water in the system
Vents maintain proper pressure in drainage lines, preventing traps
from being emptied.
4. A backflow preventer is required when:
A. Connecting a water heater
B. There is a potential for cross-connection with contaminated
water
C. Installing a new faucet
D. Replacing a drain pipe
This prevents contamination of the potable water supply.
5. What is the typical maximum spacing for supports on a 2-inch PVC
drain line?
A. 2 feet
B. 3 feet
C. 4 feet
D. 6 feet
Proper support prevents sagging and ensures proper drainage.
6. The term "DWV" in plumbing stands for:
A. Direct Water Valve
B. Domestic Water Vent
C. Drain, Waste, and Vent
D. Dual Water Valve
DWV systems manage all non-pressurized plumbing flows in a
building.
7. Which material is most commonly used for underground water
supply lines?
A. Copper
, B. PEX
C. Cast iron
D. Galvanized steel
PEX is flexible, resistant to corrosion, and easy to install
underground.
8. Which fixture requires a trap?
A. Water heater
B. Sink
C. Water meter
D. Boiler
Traps prevent sewer gases from entering living spaces.
9. What is the purpose of a pressure-reducing valve?
A. Increase flow
B. Lower incoming water pressure to safe levels
C. Divert water
D. Measure water usage
High pressure can damage plumbing fixtures and appliances.
10. The maximum distance a water closet trap arm can extend
without venting is:
A. 12 inches
B. 24 inches
C. 30 inches
D. 36 inches
Venting prevents siphoning and ensures proper trap function.
11. What is the standard water supply pipe size for a residential
kitchen sink?
A. 1/2 inch
