California Plumbing Contractor (C-
36) Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. Which piping material is commonly approved for potable cold-
water distribution when installed in accordance with applicable
plumbing requirements?
A. Unrated garden hose
B. Copper tube approved for potable-water use
C. Automotive fuel hose
D. Non-potable drainage tubing
Answer: B. Copper tube approved for potable-water use
Rationale: Copper tube manufactured and approved for potable-water
service is widely used in plumbing systems because it provides suitable
durability, pressure resistance, and compatibility with potable water.
The material must still be correctly sized, joined, supported, and
installed according to the applicable code and manufacturer
requirements.
2. What is the primary function of a plumbing trap?
A. Increase water pressure
B. Prevent pipe expansion
C. Maintain a water seal that helps prevent sewer gases from
,entering a building
D. Increase drainage velocity
Answer: C. Maintain a water seal that helps prevent sewer gases
from entering a building
Answer: C. Maintain a water seal that helps prevent sewer gases
from entering a building
Rationale: A plumbing trap retains a quantity of water that forms a
seal between the drainage system and the occupied space. The trap
must be properly designed and vented so that pressure fluctuations do
not cause the trap seal to be siphoned or blown out.
3. Which fitting is generally used to change the direction of a
drainage pipe while maintaining a relatively smooth flow path?
A. Long-sweep drainage elbow
B. Sharp 90-degree pressure elbow
C. Cap
D. Coupling
Answer: A. Long-sweep drainage elbow
Rationale: Long-sweep fittings provide a smoother change of direction
than abrupt fittings and are therefore appropriate for many drainage
applications. Drainage fittings are designed with flow characteristics
different from fittings intended primarily for pressurized water
systems.
4. What is the purpose of a vent system in a sanitary drainage
system?
A. Supply drinking water
B. Increase water-heater temperature
C. Filter wastewater
,D. Protect trap seals and provide circulation of air through the
drainage system
Answer: D. Protect trap seals and provide circulation of air through
the drainage system
Rationale: Drainage vents help equalize pressure within the drainage
piping and protect trap seals from siphonage and excessive pressure.
Proper venting also promotes reliable drainage-system operation.
5. A fixture drain connects a plumbing fixture to which portion of the
drainage system?
A. Water-service line
B. Drainage piping leading toward the building drain
C. Gas piping
D. Electrical grounding system
Answer: B. Drainage piping leading toward the building drain
Rationale: The fixture drain carries discharge from a fixture to the
drainage system. It is part of the drainage pathway and must be sized,
sloped, connected, and vented as required by applicable plumbing
provisions.
6. What is the main purpose of a cleanout?
A. Regulate water pressure
B. Provide access to drainage piping for inspection and cleaning
C. Prevent water hammer
D. Measure gas pressure
Answer: B. Provide access to drainage piping for inspection and
cleaning
, Rationale: Cleanouts allow plumbers to access drainage piping when
blockages or maintenance problems occur. They must be located and
sized appropriately and remain accessible after construction.
7. Which condition is most likely to cause a water hammer problem?
A. Low drain slope
B. Rapidly closing a valve in a pressurized water line
C. Oversized sewer vent
D. Open cleanout
Answer: B. Rapidly closing a valve in a pressurized water line
Rationale: Water hammer is a pressure surge caused by a sudden
change in water velocity. Quick-closing valves can produce significant
pressure waves. Proper piping design, secure supports, controlled valve
operation, and approved water-hammer arresting devices can help
control the problem where required.
8. What is the purpose of a pressure-reducing valve on a water-supply
system?
A. Increase drainage flow
B. Remove sewer gases
C. Reduce excessive incoming water pressure to an acceptable
downstream pressure
D. Heat potable water
Answer: C. Reduce excessive incoming water pressure to an
acceptable downstream pressure
Rationale: A pressure-reducing valve controls excessive supply
pressure so that downstream plumbing fixtures, appliances, and piping
operate within their permitted pressure range. Excessive pressure can
contribute to leakage, fixture damage, and water hammer.
36) Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. Which piping material is commonly approved for potable cold-
water distribution when installed in accordance with applicable
plumbing requirements?
A. Unrated garden hose
B. Copper tube approved for potable-water use
C. Automotive fuel hose
D. Non-potable drainage tubing
Answer: B. Copper tube approved for potable-water use
Rationale: Copper tube manufactured and approved for potable-water
service is widely used in plumbing systems because it provides suitable
durability, pressure resistance, and compatibility with potable water.
The material must still be correctly sized, joined, supported, and
installed according to the applicable code and manufacturer
requirements.
2. What is the primary function of a plumbing trap?
A. Increase water pressure
B. Prevent pipe expansion
C. Maintain a water seal that helps prevent sewer gases from
,entering a building
D. Increase drainage velocity
Answer: C. Maintain a water seal that helps prevent sewer gases
from entering a building
Answer: C. Maintain a water seal that helps prevent sewer gases
from entering a building
Rationale: A plumbing trap retains a quantity of water that forms a
seal between the drainage system and the occupied space. The trap
must be properly designed and vented so that pressure fluctuations do
not cause the trap seal to be siphoned or blown out.
3. Which fitting is generally used to change the direction of a
drainage pipe while maintaining a relatively smooth flow path?
A. Long-sweep drainage elbow
B. Sharp 90-degree pressure elbow
C. Cap
D. Coupling
Answer: A. Long-sweep drainage elbow
Rationale: Long-sweep fittings provide a smoother change of direction
than abrupt fittings and are therefore appropriate for many drainage
applications. Drainage fittings are designed with flow characteristics
different from fittings intended primarily for pressurized water
systems.
4. What is the purpose of a vent system in a sanitary drainage
system?
A. Supply drinking water
B. Increase water-heater temperature
C. Filter wastewater
,D. Protect trap seals and provide circulation of air through the
drainage system
Answer: D. Protect trap seals and provide circulation of air through
the drainage system
Rationale: Drainage vents help equalize pressure within the drainage
piping and protect trap seals from siphonage and excessive pressure.
Proper venting also promotes reliable drainage-system operation.
5. A fixture drain connects a plumbing fixture to which portion of the
drainage system?
A. Water-service line
B. Drainage piping leading toward the building drain
C. Gas piping
D. Electrical grounding system
Answer: B. Drainage piping leading toward the building drain
Rationale: The fixture drain carries discharge from a fixture to the
drainage system. It is part of the drainage pathway and must be sized,
sloped, connected, and vented as required by applicable plumbing
provisions.
6. What is the main purpose of a cleanout?
A. Regulate water pressure
B. Provide access to drainage piping for inspection and cleaning
C. Prevent water hammer
D. Measure gas pressure
Answer: B. Provide access to drainage piping for inspection and
cleaning
, Rationale: Cleanouts allow plumbers to access drainage piping when
blockages or maintenance problems occur. They must be located and
sized appropriately and remain accessible after construction.
7. Which condition is most likely to cause a water hammer problem?
A. Low drain slope
B. Rapidly closing a valve in a pressurized water line
C. Oversized sewer vent
D. Open cleanout
Answer: B. Rapidly closing a valve in a pressurized water line
Rationale: Water hammer is a pressure surge caused by a sudden
change in water velocity. Quick-closing valves can produce significant
pressure waves. Proper piping design, secure supports, controlled valve
operation, and approved water-hammer arresting devices can help
control the problem where required.
8. What is the purpose of a pressure-reducing valve on a water-supply
system?
A. Increase drainage flow
B. Remove sewer gases
C. Reduce excessive incoming water pressure to an acceptable
downstream pressure
D. Heat potable water
Answer: C. Reduce excessive incoming water pressure to an
acceptable downstream pressure
Rationale: A pressure-reducing valve controls excessive supply
pressure so that downstream plumbing fixtures, appliances, and piping
operate within their permitted pressure range. Excessive pressure can
contribute to leakage, fixture damage, and water hammer.
