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Missouri Plumbing Contractor
Examination Practice Exam Questions
And 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
B. To remove solid waste
C. To prevent sewer gases from entering the building
D. To filter drinking water
Rationale: Vent systems equalize pressure in the drainage system and safely
vent sewer gases outdoors.
2. Which pipe material is commonly approved for residential water
distribution systems?
A. Clay pipe
B. Copper tubing
C. Cast iron soil pipe
D. Concrete pipe
Rationale: Copper tubing is durable, corrosion-resistant, and commonly
approved for potable water supply systems.
, 3. What fixture is required to have a water seal to block sewer gases?
A. Cleanout
B. Vent stack
C. Trap
D. Pressure regulator
Rationale: A trap maintains a water seal that prevents sewer gases from
entering occupied spaces.
4. What is the minimum slope generally required for horizontal drainage
piping 3 inches or smaller?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1 inch per foot
Rationale: Plumbing codes commonly require a slope of 1/4 inch per foot for
effective drainage in smaller piping.
5. Which valve is commonly installed to prevent backflow into a potable water
system?
A. Gate valve
B. Globe valve
C. Ball valve
D. Check valve
Rationale: Check valves prevent reverse flow that could contaminate potable
water systems.
6. What is the purpose of an air gap?
A. To increase drainage flow
B. To support piping
C. To prevent back siphonage
D. To reduce water temperature
, Rationale: An air gap provides a physical separation that prevents contaminated
water from siphoning into clean water systems.
7. Which plumbing fixture typically requires the largest drainage pipe?
A. Lavatory
B. Dishwasher
C. Shower
D. Water closet
Rationale: Water closets discharge solid waste and require larger drainage
piping capacity.
8. What type of joint is commonly used for copper water tubing?
A. Threaded joint
B. Solvent cement joint
C. Soldered joint
D. Compression sleeve only
Rationale: Soldered joints are widely used for securely joining copper tubing.
9. Which fitting is used to change the direction of piping by 90 degrees?
A. Coupling
B. Tee
C. Reducer
D. Elbow
Rationale: Elbows are specifically designed to change pipe direction.
10.What is the function of a pressure-reducing valve?
A. Increase flow rate
B. Remove sediment
C. Lower excessive water pressure
D. Stop water hammer
Rationale: Pressure-reducing valves protect plumbing systems from excessive
municipal supply pressure.
Missouri Plumbing Contractor
Examination Practice Exam Questions
And 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
B. To remove solid waste
C. To prevent sewer gases from entering the building
D. To filter drinking water
Rationale: Vent systems equalize pressure in the drainage system and safely
vent sewer gases outdoors.
2. Which pipe material is commonly approved for residential water
distribution systems?
A. Clay pipe
B. Copper tubing
C. Cast iron soil pipe
D. Concrete pipe
Rationale: Copper tubing is durable, corrosion-resistant, and commonly
approved for potable water supply systems.
, 3. What fixture is required to have a water seal to block sewer gases?
A. Cleanout
B. Vent stack
C. Trap
D. Pressure regulator
Rationale: A trap maintains a water seal that prevents sewer gases from
entering occupied spaces.
4. What is the minimum slope generally required for horizontal drainage
piping 3 inches or smaller?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1 inch per foot
Rationale: Plumbing codes commonly require a slope of 1/4 inch per foot for
effective drainage in smaller piping.
5. Which valve is commonly installed to prevent backflow into a potable water
system?
A. Gate valve
B. Globe valve
C. Ball valve
D. Check valve
Rationale: Check valves prevent reverse flow that could contaminate potable
water systems.
6. What is the purpose of an air gap?
A. To increase drainage flow
B. To support piping
C. To prevent back siphonage
D. To reduce water temperature
, Rationale: An air gap provides a physical separation that prevents contaminated
water from siphoning into clean water systems.
7. Which plumbing fixture typically requires the largest drainage pipe?
A. Lavatory
B. Dishwasher
C. Shower
D. Water closet
Rationale: Water closets discharge solid waste and require larger drainage
piping capacity.
8. What type of joint is commonly used for copper water tubing?
A. Threaded joint
B. Solvent cement joint
C. Soldered joint
D. Compression sleeve only
Rationale: Soldered joints are widely used for securely joining copper tubing.
9. Which fitting is used to change the direction of piping by 90 degrees?
A. Coupling
B. Tee
C. Reducer
D. Elbow
Rationale: Elbows are specifically designed to change pipe direction.
10.What is the function of a pressure-reducing valve?
A. Increase flow rate
B. Remove sediment
C. Lower excessive water pressure
D. Stop water hammer
Rationale: Pressure-reducing valves protect plumbing systems from excessive
municipal supply pressure.
