MASTER PLUMBER LICENSING EXAM
QUESTION AND CORRECT
ANSWERS(VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A INSTANT
DOWNLOAD PDF
1. What is the primary purpose of a plumbing vent system?
A. Increase water pressure
B. Prevent pipe corrosion
C. Allow air into the drainage system
D. Remove solid waste
Answer: C
Rationale: Venting prevents siphonage of traps by equalizing air pressure
in the drainage system.
2. The minimum slope for a 3-inch horizontal drainage 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
Answer: B
Rationale: Codes typically allow 1/8 inch per foot for 3-inch or larger
drainage piping.
3. Which fitting is used to connect a horizontal branch to a vertical stack?
A. Tee
B. Cross
C. Wye
D. Coupling
Answer: C
, Rationale: A wye fitting directs flow smoothly into the vertical stack,
reducing turbulence.
4. What device prevents backflow in potable water systems?
A. Gate valve
B. Pressure regulator
C. Backflow preventer
D. Check valve only
Answer: C
Rationale: Backflow preventers protect potable water from
contamination due to reverse flow.
5. The purpose of a trap seal is to:
A. Increase drainage speed
B. Prevent sewer gases from entering the building
C. Improve venting
D. Reduce water usage
Answer: B
Rationale: The water seal blocks sewer gases from traveling back into
occupied spaces.
6. Which material is most commonly used for residential water supply piping
today?
A. Galvanized steel
B. Cast iron
C. PEX
D. Lead
Answer: C
Rationale: PEX is flexible, corrosion-resistant, and easy to install.
7. What is the minimum trap seal depth for most plumbing fixtures?
A. 1/2 inch
B. 1 inch
C. 2 inches
D. 4 inches
Answer: C
, Rationale: Codes generally require a minimum 2-inch trap seal to prevent
evaporation.
8. Which valve is best for throttling flow?
A. Ball valve
B. Globe valve
C. Gate valve
D. Check valve
Answer: B
Rationale: Globe valves are designed to regulate and control flow
accurately.
9. What type of joint is commonly used with copper tubing?
A. Threaded
B. Soldered (sweat)
C. Glued
D. Welded
Answer: B
Rationale: Copper tubing is typically joined using soldered connections.
10.Which fixture requires the largest drain size?
A. Lavatory
B. Shower
C. Water closet
D. Bidet
Answer: C
Rationale: Water closets require larger drains due to solid waste
discharge.
11.What is the function of a cleanout?
A. Vent the system
B. Regulate pressure
C. Provide access for cleaning drainage pipes
D. Prevent backflow
Answer: C
Rationale: Cleanouts allow maintenance and removal of blockages.
QUESTION AND CORRECT
ANSWERS(VERIFIED ANSWERS) PLUS
RATIONALES 2026 Q&A INSTANT
DOWNLOAD PDF
1. What is the primary purpose of a plumbing vent system?
A. Increase water pressure
B. Prevent pipe corrosion
C. Allow air into the drainage system
D. Remove solid waste
Answer: C
Rationale: Venting prevents siphonage of traps by equalizing air pressure
in the drainage system.
2. The minimum slope for a 3-inch horizontal drainage 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
Answer: B
Rationale: Codes typically allow 1/8 inch per foot for 3-inch or larger
drainage piping.
3. Which fitting is used to connect a horizontal branch to a vertical stack?
A. Tee
B. Cross
C. Wye
D. Coupling
Answer: C
, Rationale: A wye fitting directs flow smoothly into the vertical stack,
reducing turbulence.
4. What device prevents backflow in potable water systems?
A. Gate valve
B. Pressure regulator
C. Backflow preventer
D. Check valve only
Answer: C
Rationale: Backflow preventers protect potable water from
contamination due to reverse flow.
5. The purpose of a trap seal is to:
A. Increase drainage speed
B. Prevent sewer gases from entering the building
C. Improve venting
D. Reduce water usage
Answer: B
Rationale: The water seal blocks sewer gases from traveling back into
occupied spaces.
6. Which material is most commonly used for residential water supply piping
today?
A. Galvanized steel
B. Cast iron
C. PEX
D. Lead
Answer: C
Rationale: PEX is flexible, corrosion-resistant, and easy to install.
7. What is the minimum trap seal depth for most plumbing fixtures?
A. 1/2 inch
B. 1 inch
C. 2 inches
D. 4 inches
Answer: C
, Rationale: Codes generally require a minimum 2-inch trap seal to prevent
evaporation.
8. Which valve is best for throttling flow?
A. Ball valve
B. Globe valve
C. Gate valve
D. Check valve
Answer: B
Rationale: Globe valves are designed to regulate and control flow
accurately.
9. What type of joint is commonly used with copper tubing?
A. Threaded
B. Soldered (sweat)
C. Glued
D. Welded
Answer: B
Rationale: Copper tubing is typically joined using soldered connections.
10.Which fixture requires the largest drain size?
A. Lavatory
B. Shower
C. Water closet
D. Bidet
Answer: C
Rationale: Water closets require larger drains due to solid waste
discharge.
11.What is the function of a cleanout?
A. Vent the system
B. Regulate pressure
C. Provide access for cleaning drainage pipes
D. Prevent backflow
Answer: C
Rationale: Cleanouts allow maintenance and removal of blockages.
