AZ C-37 (CR-37) Plumbing Contractor Practice Exam
Questions
And Correct ANSWER>✔-s (Verified
ANSWER>✔-s) Plus Rationale 2026 Q&A
1. What is the primary purpose of a trap in a plumbing fixture?
A) To filter debris from wastewater
B) To prevent sewer gases from entering the building
C) To regulate water flow
D) To reduce water consumption
Correct ANSWER>✔-: B
Rationale: A trap maintains a water seal that blocks sewer gases from entering the building, ensuring a
sanitary, odor-free interior. Option A is incorrect because traps are not designed for debris filtration.
Option C is incorrect because traps do not regulate water flow. Option D is incorrect because traps do
not reduce water consumption.
2. Which type of trap is most commonly used under a lavatory sink?
A) S-trap
B) P-trap
C) Drum trap
D) Bell trap
,Correct ANSWER>✔-: B
Rationale: P-traps are the standard under sinks because they reliably maintain a water seal, are easy to
clean and maintain, and comply with modern plumbing code requirements. Option A is incorrect
because S-traps are outdated and often prohibited by code. Option C is incorrect because drum traps
are used primarily in older bathtub installations. Option D is incorrect because bell traps are typically
used in floor drains.
3. In a drainage system, what is the purpose of a vent pipe?
A) To carry waste to the sewer
B) To provide a path for heat to escape
C) To filter waste before disposal
D) To allow fresh air into the system to prevent vacuum formation and prevent siphoning of traps
Correct ANSWER>✔-: D
Rationale: Vent pipes equalize air pressure in drain-waste-vent (DWV) systems, preventing trap
siphonage and allowing wastewater to flow smoothly. Option A is incorrect because drain pipes carry
waste, not vent pipes. Option B is incorrect because vent pipes are not designed for heat dissipation.
Option C is incorrect because vent pipes do not filter waste.
4. Which material is most suitable for drainage-waste-vent (DWV) piping in many plumbing installations?
A) PVC
B) ABS
C) Cast iron
D) Copper
Correct ANSWER>✔-: C
Rationale: Cast iron is durable, handles heat well, and is commonly used in commercial or heavy-duty
DWV systems — especially where rigidity and fire-resistance matter. Option A is incorrect because PVC
is used in residential but not always in commercial. Option B is incorrect because ABS is less durable
than cast iron. Option D is incorrect because copper is primarily for supply lines, not DWV.
,5. What is the minimum diameter commonly used for a residential bathroom sink (lavatory) drain line
under typical plumbing code?
A) 1 inch
B) 1.25 inches
C) 1.5 inches
D) 2 inches
Correct ANSWER>✔-: C
Rationale: A 1.5-inch drain line gives adequate capacity for typical sink waste water flow and is widely
accepted under plumbing codes for lavatories. Option A is incorrect because 1 inch is too small for any
fixture drain. Option B is incorrect because 1.25 inches is below code minimum. Option D is incorrect
because 2 inches is larger than required for a lavatory.
6. What is the function of a cleanout in a drainage system?
A) To prevent backflow of waste into the fixture
B) To provide access for cleaning and maintaining the drainage system
C) To allow connection of additional fixtures
D) To filter waste before disposal
Correct ANSWER>✔-: B
Rationale: Cleanouts provide maintenance access so blockages or buildup can be cleared — essential for
maintaining system function over time. Option A is incorrect because backflow prevention devices
handle that function. Option C is incorrect because cleanouts are not used for fixture connections.
Option D is incorrect because cleanouts do not filter waste.
7. What is the typical slope required for a horizontal drainage pipe to ensure proper flow?
A) Level / no slope
, B) 1/16 inch per foot
C) 1/8 inch per foot
D) 1/2 inch per foot
Correct ANSWER>✔-: C
Rationale: A slope of 1/8 inch per foot is generally acceptable for gravity-assisted flow without excessive
velocity or risk of siphoning. Option A is incorrect because level pipes cause stagnant water. Option B is
incorrect because 1/16 inch per foot is insufficient for most installations. Option D is incorrect because
1/2 inch per foot may cause excessive water velocity.
8. What device is used to prevent backflow in a plumbing system?
A) Pressure regulator
B) Backflow preventer
C) Check valve
D) Both B and C
Correct ANSWER>✔-: D
Rationale: Both backflow preventers and check valves prevent reverse flow of water. A backflow
preventer is a comprehensive assembly while a check valve is a simpler device. Option A is incorrect
because pressure regulators control water pressure, not backflow. Option C alone is incomplete because
backflow preventers also serve this function.
9. What is the maximum distance a trap can be from a vent pipe under most plumbing codes?
A) 2 feet
B) 4 feet
C) 6 feet
D) 8 feet
Correct ANSWER>✔-: C
Questions
And Correct ANSWER>✔-s (Verified
ANSWER>✔-s) Plus Rationale 2026 Q&A
1. What is the primary purpose of a trap in a plumbing fixture?
A) To filter debris from wastewater
B) To prevent sewer gases from entering the building
C) To regulate water flow
D) To reduce water consumption
Correct ANSWER>✔-: B
Rationale: A trap maintains a water seal that blocks sewer gases from entering the building, ensuring a
sanitary, odor-free interior. Option A is incorrect because traps are not designed for debris filtration.
Option C is incorrect because traps do not regulate water flow. Option D is incorrect because traps do
not reduce water consumption.
2. Which type of trap is most commonly used under a lavatory sink?
A) S-trap
B) P-trap
C) Drum trap
D) Bell trap
,Correct ANSWER>✔-: B
Rationale: P-traps are the standard under sinks because they reliably maintain a water seal, are easy to
clean and maintain, and comply with modern plumbing code requirements. Option A is incorrect
because S-traps are outdated and often prohibited by code. Option C is incorrect because drum traps
are used primarily in older bathtub installations. Option D is incorrect because bell traps are typically
used in floor drains.
3. In a drainage system, what is the purpose of a vent pipe?
A) To carry waste to the sewer
B) To provide a path for heat to escape
C) To filter waste before disposal
D) To allow fresh air into the system to prevent vacuum formation and prevent siphoning of traps
Correct ANSWER>✔-: D
Rationale: Vent pipes equalize air pressure in drain-waste-vent (DWV) systems, preventing trap
siphonage and allowing wastewater to flow smoothly. Option A is incorrect because drain pipes carry
waste, not vent pipes. Option B is incorrect because vent pipes are not designed for heat dissipation.
Option C is incorrect because vent pipes do not filter waste.
4. Which material is most suitable for drainage-waste-vent (DWV) piping in many plumbing installations?
A) PVC
B) ABS
C) Cast iron
D) Copper
Correct ANSWER>✔-: C
Rationale: Cast iron is durable, handles heat well, and is commonly used in commercial or heavy-duty
DWV systems — especially where rigidity and fire-resistance matter. Option A is incorrect because PVC
is used in residential but not always in commercial. Option B is incorrect because ABS is less durable
than cast iron. Option D is incorrect because copper is primarily for supply lines, not DWV.
,5. What is the minimum diameter commonly used for a residential bathroom sink (lavatory) drain line
under typical plumbing code?
A) 1 inch
B) 1.25 inches
C) 1.5 inches
D) 2 inches
Correct ANSWER>✔-: C
Rationale: A 1.5-inch drain line gives adequate capacity for typical sink waste water flow and is widely
accepted under plumbing codes for lavatories. Option A is incorrect because 1 inch is too small for any
fixture drain. Option B is incorrect because 1.25 inches is below code minimum. Option D is incorrect
because 2 inches is larger than required for a lavatory.
6. What is the function of a cleanout in a drainage system?
A) To prevent backflow of waste into the fixture
B) To provide access for cleaning and maintaining the drainage system
C) To allow connection of additional fixtures
D) To filter waste before disposal
Correct ANSWER>✔-: B
Rationale: Cleanouts provide maintenance access so blockages or buildup can be cleared — essential for
maintaining system function over time. Option A is incorrect because backflow prevention devices
handle that function. Option C is incorrect because cleanouts are not used for fixture connections.
Option D is incorrect because cleanouts do not filter waste.
7. What is the typical slope required for a horizontal drainage pipe to ensure proper flow?
A) Level / no slope
, B) 1/16 inch per foot
C) 1/8 inch per foot
D) 1/2 inch per foot
Correct ANSWER>✔-: C
Rationale: A slope of 1/8 inch per foot is generally acceptable for gravity-assisted flow without excessive
velocity or risk of siphoning. Option A is incorrect because level pipes cause stagnant water. Option B is
incorrect because 1/16 inch per foot is insufficient for most installations. Option D is incorrect because
1/2 inch per foot may cause excessive water velocity.
8. What device is used to prevent backflow in a plumbing system?
A) Pressure regulator
B) Backflow preventer
C) Check valve
D) Both B and C
Correct ANSWER>✔-: D
Rationale: Both backflow preventers and check valves prevent reverse flow of water. A backflow
preventer is a comprehensive assembly while a check valve is a simpler device. Option A is incorrect
because pressure regulators control water pressure, not backflow. Option C alone is incomplete because
backflow preventers also serve this function.
9. What is the maximum distance a trap can be from a vent pipe under most plumbing codes?
A) 2 feet
B) 4 feet
C) 6 feet
D) 8 feet
Correct ANSWER>✔-: C
