Master Plumber Licensing Examination
Questions With Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a trap in a plumbing system?
A. To increase water pressure
B. To prevent sewer gases from entering the building
C. To increase drainage speed
D. To filter solids from wastewater
Answer: B
Rationale: A trap is a curved section of pipe designed to hold a
small amount of water, creating a seal that blocks sewer gases
from backing up into the building while still allowing wastewater
to pass through.
2. What is the standard minimum slope for a 3-inch horizontal drain
pipe?
A. 1/16 inch per foot
B. 1/8 inch per foot
, C. 1/4 inch per foot
D. 1 inch per foot
Answer: B
Rationale: A 3-inch drain typically requires a slope of 1/8 inch
per foot to ensure proper flow velocity while preventing solids
from settling in the pipe.
3. Which material is most commonly used for DWV (Drain, Waste,
and Vent) piping today?
A. Copper
B. Cast iron
C. PVC
D. Steel
Answer: C
Rationale: PVC is widely used in DWV systems due to its
corrosion resistance, low cost, ease of installation, and smooth
interior surface that promotes efficient flow.
4. What is the function of a vent pipe in a plumbing system?
A. To increase water pressure
B. To supply air to maintain atmospheric pressure in drainage
pipes
C. To carry wastewater to the sewer
, D. To filter solids
Answer: B
Rationale: Vent pipes allow air into the drainage system,
preventing vacuum formation and ensuring smooth drainage by
maintaining atmospheric pressure.
5. What device prevents backflow in potable water systems?
A. Gate valve
B. Check valve
C. Globe valve
D. Air vent
Answer: B
Rationale: A check valve allows water to flow in only one
direction, preventing contaminated water from flowing back into
the clean water supply.
6. What is the typical color code for cold water piping in plumbing
systems?
A. Red
B. Blue
C. Green
D. Yellow
Answer: B
, Rationale: Blue is universally used to identify cold water lines,
helping plumbers and inspectors quickly distinguish between hot
and cold water systems.
7. What is the main purpose of a cleanout in a drainage system?
A. Increase water flow
B. Provide access for removing blockages
C. Regulate water pressure
D. Filter wastewater
Answer: B
Rationale: Cleanouts provide access points for plumbers to
inspect, clean, and remove obstructions from drainage piping
systems.
8. Which pipe is most suitable for underground water service lines?
A. PVC Schedule 40
B. Galvanized steel
C. Lead pipe
D. Cast iron soil pipe
Answer: A
Rationale: PVC Schedule 40 is durable, corrosion-resistant, and
widely used for underground water service lines due to its long
service life.
Questions With Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a trap in a plumbing system?
A. To increase water pressure
B. To prevent sewer gases from entering the building
C. To increase drainage speed
D. To filter solids from wastewater
Answer: B
Rationale: A trap is a curved section of pipe designed to hold a
small amount of water, creating a seal that blocks sewer gases
from backing up into the building while still allowing wastewater
to pass through.
2. What is the standard minimum slope for a 3-inch horizontal drain
pipe?
A. 1/16 inch per foot
B. 1/8 inch per foot
, C. 1/4 inch per foot
D. 1 inch per foot
Answer: B
Rationale: A 3-inch drain typically requires a slope of 1/8 inch
per foot to ensure proper flow velocity while preventing solids
from settling in the pipe.
3. Which material is most commonly used for DWV (Drain, Waste,
and Vent) piping today?
A. Copper
B. Cast iron
C. PVC
D. Steel
Answer: C
Rationale: PVC is widely used in DWV systems due to its
corrosion resistance, low cost, ease of installation, and smooth
interior surface that promotes efficient flow.
4. What is the function of a vent pipe in a plumbing system?
A. To increase water pressure
B. To supply air to maintain atmospheric pressure in drainage
pipes
C. To carry wastewater to the sewer
, D. To filter solids
Answer: B
Rationale: Vent pipes allow air into the drainage system,
preventing vacuum formation and ensuring smooth drainage by
maintaining atmospheric pressure.
5. What device prevents backflow in potable water systems?
A. Gate valve
B. Check valve
C. Globe valve
D. Air vent
Answer: B
Rationale: A check valve allows water to flow in only one
direction, preventing contaminated water from flowing back into
the clean water supply.
6. What is the typical color code for cold water piping in plumbing
systems?
A. Red
B. Blue
C. Green
D. Yellow
Answer: B
, Rationale: Blue is universally used to identify cold water lines,
helping plumbers and inspectors quickly distinguish between hot
and cold water systems.
7. What is the main purpose of a cleanout in a drainage system?
A. Increase water flow
B. Provide access for removing blockages
C. Regulate water pressure
D. Filter wastewater
Answer: B
Rationale: Cleanouts provide access points for plumbers to
inspect, clean, and remove obstructions from drainage piping
systems.
8. Which pipe is most suitable for underground water service lines?
A. PVC Schedule 40
B. Galvanized steel
C. Lead pipe
D. Cast iron soil pipe
Answer: A
Rationale: PVC Schedule 40 is durable, corrosion-resistant, and
widely used for underground water service lines due to its long
service life.
