California Plumbing Contractor Examination
(C-36) Questions With Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the primary purpose of a plumbing vent system?
A) To increase water pressure in pipes
B) To protect trap seals by equalizing air pressure in the drainage
system
C) To remove solid waste from drainage lines
D) To heat water before it enters fixtures
Rationale: The vent system allows air into the drainage piping,
preventing vacuum conditions that could siphon water out of traps.
This maintains trap seals and prevents sewer gases from entering the
building.
2. Which pipe material is commonly used for underground drainage
in modern plumbing systems?
,A) Copper Type L
B) PVC Schedule 40
C) Galvanized steel
D) Cast iron hubless only above ground
Rationale: PVC Schedule 40 is widely used for underground drainage
due to its corrosion resistance, durability, and ease of installation
compared to metallic piping.
3. What is the minimum slope required for a 4-inch horizontal
drainage pipe?
A) 1/16 inch per foot
B) 1/4 inch per foot
C) 1/8 inch per foot
D) 1 inch per foot
Rationale: Most plumbing codes require a minimum slope of 1/8 inch
per foot for 4-inch horizontal drainage piping to ensure proper flow
and prevent solids from settling.
4. What device prevents backflow into potable water systems?
,A) Gate valve
B) Air admittance valve
C) Backflow preventer
D) Check valve only
Rationale: A backflow preventer is specifically designed to prevent
contaminated water from reversing direction and entering potable
water systems.
5. Which tool is used to cut internal threads into metal pipe?
A) Pipe wrench
B) Tubing cutter
C) Pipe tap and die set
D) Reamer
Rationale: A tap and die set is used to create internal and external
threads on metal piping for threaded connections.
6. What is the function of a trap in a plumbing system?
A) To increase water flow speed
B) To filter sediment from water
, C) To prevent sewer gases from entering the building
D) To increase pipe pressure
Rationale: A trap holds a water seal that blocks sewer gases from
entering occupied spaces while allowing wastewater to pass.
7. Which fitting is used to change pipe direction by 90 degrees?
A) Tee
B) Elbow
C) Coupling
D) Reducer
Rationale: An elbow fitting is specifically designed to change the
direction of piping, commonly at 90 or 45 degrees.
8. What is the main purpose of a cleanout in a drainage system?
A) To increase flow rate
B) To provide access for clearing blockages
C) To regulate water temperature
D) To increase pipe pressure
(C-36) Questions With Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the primary purpose of a plumbing vent system?
A) To increase water pressure in pipes
B) To protect trap seals by equalizing air pressure in the drainage
system
C) To remove solid waste from drainage lines
D) To heat water before it enters fixtures
Rationale: The vent system allows air into the drainage piping,
preventing vacuum conditions that could siphon water out of traps.
This maintains trap seals and prevents sewer gases from entering the
building.
2. Which pipe material is commonly used for underground drainage
in modern plumbing systems?
,A) Copper Type L
B) PVC Schedule 40
C) Galvanized steel
D) Cast iron hubless only above ground
Rationale: PVC Schedule 40 is widely used for underground drainage
due to its corrosion resistance, durability, and ease of installation
compared to metallic piping.
3. What is the minimum slope required for a 4-inch horizontal
drainage pipe?
A) 1/16 inch per foot
B) 1/4 inch per foot
C) 1/8 inch per foot
D) 1 inch per foot
Rationale: Most plumbing codes require a minimum slope of 1/8 inch
per foot for 4-inch horizontal drainage piping to ensure proper flow
and prevent solids from settling.
4. What device prevents backflow into potable water systems?
,A) Gate valve
B) Air admittance valve
C) Backflow preventer
D) Check valve only
Rationale: A backflow preventer is specifically designed to prevent
contaminated water from reversing direction and entering potable
water systems.
5. Which tool is used to cut internal threads into metal pipe?
A) Pipe wrench
B) Tubing cutter
C) Pipe tap and die set
D) Reamer
Rationale: A tap and die set is used to create internal and external
threads on metal piping for threaded connections.
6. What is the function of a trap in a plumbing system?
A) To increase water flow speed
B) To filter sediment from water
, C) To prevent sewer gases from entering the building
D) To increase pipe pressure
Rationale: A trap holds a water seal that blocks sewer gases from
entering occupied spaces while allowing wastewater to pass.
7. Which fitting is used to change pipe direction by 90 degrees?
A) Tee
B) Elbow
C) Coupling
D) Reducer
Rationale: An elbow fitting is specifically designed to change the
direction of piping, commonly at 90 or 45 degrees.
8. What is the main purpose of a cleanout in a drainage system?
A) To increase flow rate
B) To provide access for clearing blockages
C) To regulate water temperature
D) To increase pipe pressure
