AL PL Plumbing Contractor Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2027
Q&A | Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Increase drainage flow
D. Prevent water hammer
Answer: B. Prevent sewer gases from entering the building
Rationale: A properly installed trap maintains a water seal that blocks
sewer gases from entering occupied spaces while allowing wastewater to
drain.
,2. Which fitting is generally used to change the direction of a drainage pipe
by approximately 90 degrees?
A. Sanitary tee
B. Wye
C. Quarter bend/elbow
D. Coupling
Answer: C. Quarter bend/elbow
Rationale: A 90-degree elbow or quarter bend changes the direction of
piping by approximately 90 degrees. Drainage systems require fittings
appropriate for maintaining proper flow.
3. What is the primary function of a plumbing vent?
A. Supply drinking water
B. Increase water pressure
C. Protect trap seals and allow air into the drainage system
D. Remove sediment from water
Answer: C. Protect trap seals and allow air into the drainage system
Rationale: Venting balances pressure in the drainage system and helps
prevent siphonage or backpressure that could destroy trap seals.
,4. Which pipe material is commonly used for potable water distribution?
A. PVC or CPVC approved for potable water
B. Cast-iron soil pipe only
C. ABS drain pipe only
D. Unapproved reclaimed pipe
Answer: A. PVC or CPVC approved for potable water
Rationale: Approved plastic piping such as properly rated PVC or CPVC can
be used for potable-water distribution when permitted by the applicable
code and manufacturer requirements.
5. What does DWV stand for?
A. Domestic Water Valve
B. Drain, Waste, and Vent
C. Drain Water Vacuum
D. Domestic Waste Vessel
Answer: B. Drain, Waste, and Vent
, Rationale: DWV refers to the piping system that carries wastewater and
sewage away from fixtures and provides ventilation for the drainage
system.
6. Why should a drainage pipe have proper slope?
A. To increase water temperature
B. To promote gravity flow and reduce solids accumulation
C. To increase water pressure
D. To eliminate the need for vents
Answer: B. To promote gravity flow and reduce solids accumulation
Rationale: Proper drainage slope allows wastewater to move by gravity
while helping prevent standing water and excessive accumulation of solids.
7. What is a cleanout primarily used for?
A. Increasing water pressure
B. Accessing drainage piping for inspection and cleaning
C. Measuring water temperature
D. Preventing backflow
Answer: B. Accessing drainage piping for inspection and cleaning
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2027
Q&A | Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Increase drainage flow
D. Prevent water hammer
Answer: B. Prevent sewer gases from entering the building
Rationale: A properly installed trap maintains a water seal that blocks
sewer gases from entering occupied spaces while allowing wastewater to
drain.
,2. Which fitting is generally used to change the direction of a drainage pipe
by approximately 90 degrees?
A. Sanitary tee
B. Wye
C. Quarter bend/elbow
D. Coupling
Answer: C. Quarter bend/elbow
Rationale: A 90-degree elbow or quarter bend changes the direction of
piping by approximately 90 degrees. Drainage systems require fittings
appropriate for maintaining proper flow.
3. What is the primary function of a plumbing vent?
A. Supply drinking water
B. Increase water pressure
C. Protect trap seals and allow air into the drainage system
D. Remove sediment from water
Answer: C. Protect trap seals and allow air into the drainage system
Rationale: Venting balances pressure in the drainage system and helps
prevent siphonage or backpressure that could destroy trap seals.
,4. Which pipe material is commonly used for potable water distribution?
A. PVC or CPVC approved for potable water
B. Cast-iron soil pipe only
C. ABS drain pipe only
D. Unapproved reclaimed pipe
Answer: A. PVC or CPVC approved for potable water
Rationale: Approved plastic piping such as properly rated PVC or CPVC can
be used for potable-water distribution when permitted by the applicable
code and manufacturer requirements.
5. What does DWV stand for?
A. Domestic Water Valve
B. Drain, Waste, and Vent
C. Drain Water Vacuum
D. Domestic Waste Vessel
Answer: B. Drain, Waste, and Vent
, Rationale: DWV refers to the piping system that carries wastewater and
sewage away from fixtures and provides ventilation for the drainage
system.
6. Why should a drainage pipe have proper slope?
A. To increase water temperature
B. To promote gravity flow and reduce solids accumulation
C. To increase water pressure
D. To eliminate the need for vents
Answer: B. To promote gravity flow and reduce solids accumulation
Rationale: Proper drainage slope allows wastewater to move by gravity
while helping prevent standing water and excessive accumulation of solids.
7. What is a cleanout primarily used for?
A. Increasing water pressure
B. Accessing drainage piping for inspection and cleaning
C. Measuring water temperature
D. Preventing backflow
Answer: B. Accessing drainage piping for inspection and cleaning
