CALIFORNIA CONTRACTORS STATE LICENSE
BOARD (CSLB) PLUMBING CONTRACTOR EXAM
QUESTIONS AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES 2026
Q&A | INSTANT DOWNLOAD PDF.
1. Which of the following is the minimum required slope for a 3-inch
horizontal drainage pipe?
A) 1/8 inch per foot
B) 1/4 inch per foot
C) 1/2 inch per foot
D) 1 inch per foot
B) 1/4 inch per foot
This slope ensures proper drainage and prevents standing water in a 3-
inch horizontal pipe, as required by the California Plumbing Code.
2. What type of pipe is most commonly used for potable water supply
in residential construction?
A) Galvanized steel
B) Copper
C) PVC Schedule 40
D) Cast iron
B) Copper
Copper tubing is preferred for potable water because it is durable,
corrosion-resistant, and approved by code.
,3. A vent stack is required to extend at least how many inches above
the roof?
A) 12 inches
B) 18 inches
C) 24 inches
D) 30 inches
C) 24 inches
The vent must extend a minimum of 24 inches above the roof surface to
allow proper air circulation and prevent siphoning.
4. Which of the following valves is typically used to prevent backflow
in a plumbing system?
A) Gate valve
B) Check valve
C) Ball valve
D) Globe valve
B) Check valve
A check valve allows water to flow in only one direction, preventing
backflow.
5. What is the maximum distance a trap can be from a vent for a 1
1/4-inch pipe?
A) 2 feet
B) 3 feet
C) 4 feet
D) 5 feet
,C) 4 feet
The maximum developed length from trap to vent for a 1 1/4-inch pipe
is 4 feet according to plumbing code tables.
6. Which of the following is a required component for a water heater
installation to prevent excessive pressure?
A) Expansion tank
B) Hose bib
C) Vacuum breaker
D) Check valve
A) Expansion tank
An expansion tank prevents excessive pressure in a closed water system
when water heats and expands.
7. What is the standard test pressure for a DWV (Drain, Waste, Vent)
system?
A) 5 psi
B) 10 psi
C) 15 psi
D) 20 psi
A) 5 psi
DWV systems are low-pressure systems and are tested at 5 psi to check
for leaks.
8. What is the primary purpose of a P-trap?
, A) Facilitate water flow
B) Prevent sewer gases from entering the building
C) Increase water pressure
D) Reduce noise in piping
B) Prevent sewer gases from entering the building
The P-trap retains water in its bend, creating a seal against sewer
gases.
9. Which material is prohibited for use in residential water supply
systems in California?
A) Copper
B) Lead
C) CPVC
D) PEX
B) Lead
Lead is toxic and banned in potable water systems due to health
hazards.
10. When joining copper tubing, which of the following methods
requires the use of flux and a torch?
A) Compression fitting
B) Soldering
C) Threaded connection
D) Push-fit connection
B) Soldering
Soldering uses flux and heat to create a permanent, leak-proof joint.
BOARD (CSLB) PLUMBING CONTRACTOR EXAM
QUESTIONS AND CORRECT ANSWERS
(VERIFIED ANSWERS) PLUS RATIONALES 2026
Q&A | INSTANT DOWNLOAD PDF.
1. Which of the following is the minimum required slope for a 3-inch
horizontal drainage pipe?
A) 1/8 inch per foot
B) 1/4 inch per foot
C) 1/2 inch per foot
D) 1 inch per foot
B) 1/4 inch per foot
This slope ensures proper drainage and prevents standing water in a 3-
inch horizontal pipe, as required by the California Plumbing Code.
2. What type of pipe is most commonly used for potable water supply
in residential construction?
A) Galvanized steel
B) Copper
C) PVC Schedule 40
D) Cast iron
B) Copper
Copper tubing is preferred for potable water because it is durable,
corrosion-resistant, and approved by code.
,3. A vent stack is required to extend at least how many inches above
the roof?
A) 12 inches
B) 18 inches
C) 24 inches
D) 30 inches
C) 24 inches
The vent must extend a minimum of 24 inches above the roof surface to
allow proper air circulation and prevent siphoning.
4. Which of the following valves is typically used to prevent backflow
in a plumbing system?
A) Gate valve
B) Check valve
C) Ball valve
D) Globe valve
B) Check valve
A check valve allows water to flow in only one direction, preventing
backflow.
5. What is the maximum distance a trap can be from a vent for a 1
1/4-inch pipe?
A) 2 feet
B) 3 feet
C) 4 feet
D) 5 feet
,C) 4 feet
The maximum developed length from trap to vent for a 1 1/4-inch pipe
is 4 feet according to plumbing code tables.
6. Which of the following is a required component for a water heater
installation to prevent excessive pressure?
A) Expansion tank
B) Hose bib
C) Vacuum breaker
D) Check valve
A) Expansion tank
An expansion tank prevents excessive pressure in a closed water system
when water heats and expands.
7. What is the standard test pressure for a DWV (Drain, Waste, Vent)
system?
A) 5 psi
B) 10 psi
C) 15 psi
D) 20 psi
A) 5 psi
DWV systems are low-pressure systems and are tested at 5 psi to check
for leaks.
8. What is the primary purpose of a P-trap?
, A) Facilitate water flow
B) Prevent sewer gases from entering the building
C) Increase water pressure
D) Reduce noise in piping
B) Prevent sewer gases from entering the building
The P-trap retains water in its bend, creating a seal against sewer
gases.
9. Which material is prohibited for use in residential water supply
systems in California?
A) Copper
B) Lead
C) CPVC
D) PEX
B) Lead
Lead is toxic and banned in potable water systems due to health
hazards.
10. When joining copper tubing, which of the following methods
requires the use of flux and a torch?
A) Compression fitting
B) Soldering
C) Threaded connection
D) Push-fit connection
B) Soldering
Soldering uses flux and heat to create a permanent, leak-proof joint.
