Plumbing Contractor Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales
2025|2026 Q&A | Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
a) To increase water pressure
b) To prevent sewer gases from entering the building
c) To store water for flushing
d) To balance system pressure
Traps hold water to create a barrier that blocks sewer gases from
escaping into occupied spaces.
2. The minimum slope for a horizontal drain pipe 3 inches in diameter is:
a) 1/8 inch per foot
b) 1/4 inch per foot
c) 3/8 inch per foot
d) 1/2 inch per foot
, Code requires a slope of 1/4 inch per foot for drainage piping under 4
inches to ensure proper flow and prevent clogging.
3. What type of valve is best suited for throttling flow?
a) Gate valve
b) Globe valve
c) Ball valve
d) Check valve
Globe valves allow precise regulation of flow, making them suitable
for throttling.
4. Which type of piping is most commonly used for natural gas
distribution in buildings?
a) PVC
b) Copper type M
c) Black steel
d) Galvanized steel
Black steel pipe is the standard material for natural gas distribution
due to strength and safety.
5. What does DWV stand for in plumbing systems?
a) Drain Water Vent
b) Direct Waste Valve
c) Drain Waste Vent
d) Domestic Water Valve
, DWV refers to the system that removes wastewater and vents sewer
gases.
6. A backflow preventer is required to:
a) Prevent pipe bursts
b) Regulate pressure
c) Prevent contaminated water from entering potable water supply
d) Increase water temperature
Backflow devices protect drinking water from contamination due to
backpressure or backsiphonage.
7. Which type of copper tubing is the thickest wall?
a) Type M
b) Type L
c) Type K
d) DWV copper
Type K has the thickest walls, suitable for underground and high-
pressure applications.
8. A cleanout must be installed at intervals not exceeding:
a) 25 feet
b) 50 feet
c) 100 feet
d) 150 feet
Plumbing codes require cleanouts at 100-foot intervals in horizontal
drainage piping.
, 9. The minimum size of a vent pipe is:
a) 1/2 inch
b) 3/4 inch
c) 1 1/4 inch
d) 2 inches
Most codes specify 1 1/4 inch as the minimum vent size to allow air
circulation.
10. Which fixture requires a trap primer?
a) Lavatory
b) Shower
c) Kitchen sink
d) Floor drain
Trap primers are used on floor drains to maintain the water seal in
the trap, preventing sewer gas escape.
11. What is the maximum distance between a trap and its vent for a
2-inch pipe?
a) 3 feet
b) 5 feet
c) 8 feet
d) 10 feet
For 2-inch pipes, the trap arm can extend up to 8 feet before
requiring a vent.
Questions And Correct Answers
(Verified Answers) Plus Rationales
2025|2026 Q&A | Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
a) To increase water pressure
b) To prevent sewer gases from entering the building
c) To store water for flushing
d) To balance system pressure
Traps hold water to create a barrier that blocks sewer gases from
escaping into occupied spaces.
2. The minimum slope for a horizontal drain pipe 3 inches in diameter is:
a) 1/8 inch per foot
b) 1/4 inch per foot
c) 3/8 inch per foot
d) 1/2 inch per foot
, Code requires a slope of 1/4 inch per foot for drainage piping under 4
inches to ensure proper flow and prevent clogging.
3. What type of valve is best suited for throttling flow?
a) Gate valve
b) Globe valve
c) Ball valve
d) Check valve
Globe valves allow precise regulation of flow, making them suitable
for throttling.
4. Which type of piping is most commonly used for natural gas
distribution in buildings?
a) PVC
b) Copper type M
c) Black steel
d) Galvanized steel
Black steel pipe is the standard material for natural gas distribution
due to strength and safety.
5. What does DWV stand for in plumbing systems?
a) Drain Water Vent
b) Direct Waste Valve
c) Drain Waste Vent
d) Domestic Water Valve
, DWV refers to the system that removes wastewater and vents sewer
gases.
6. A backflow preventer is required to:
a) Prevent pipe bursts
b) Regulate pressure
c) Prevent contaminated water from entering potable water supply
d) Increase water temperature
Backflow devices protect drinking water from contamination due to
backpressure or backsiphonage.
7. Which type of copper tubing is the thickest wall?
a) Type M
b) Type L
c) Type K
d) DWV copper
Type K has the thickest walls, suitable for underground and high-
pressure applications.
8. A cleanout must be installed at intervals not exceeding:
a) 25 feet
b) 50 feet
c) 100 feet
d) 150 feet
Plumbing codes require cleanouts at 100-foot intervals in horizontal
drainage piping.
, 9. The minimum size of a vent pipe is:
a) 1/2 inch
b) 3/4 inch
c) 1 1/4 inch
d) 2 inches
Most codes specify 1 1/4 inch as the minimum vent size to allow air
circulation.
10. Which fixture requires a trap primer?
a) Lavatory
b) Shower
c) Kitchen sink
d) Floor drain
Trap primers are used on floor drains to maintain the water seal in
the trap, preventing sewer gas escape.
11. What is the maximum distance between a trap and its vent for a
2-inch pipe?
a) 3 feet
b) 5 feet
c) 8 feet
d) 10 feet
For 2-inch pipes, the trap arm can extend up to 8 feet before
requiring a vent.
