Missouri Plumbing Inspection Technician
Exam Practice Questions And Correct
Answers (Verified Answers) Plus Rationale
2026 Q&A| Instant Download Pdf
1. During a plumbing inspection, which component is primarily
responsible for preventing sewer gases from entering a building
through fixtures?
A. Vent stack
B. Cleanout
C. Trap
D. Backflow preventer
The trap holds a water seal that blocks sewer gases from traveling
back into occupied spaces, making it essential for sanitation and
safety.
,2. What is the minimum slope generally required for horizontal drainage
piping of 3 inches in diameter or less?
A. 1/16 inch per foot
B. 1/4 inch per foot
C. 1/2 inch per foot
D. 1 inch per foot
A slope of 1/4 inch per foot ensures proper flow velocity to prevent
blockages without causing solids to separate from liquids.
3. Which device is required to protect potable water systems from
contamination due to backflow?
A. Pressure regulator
B. Expansion tank
C. Backflow preventer
D. Air chamber
Backflow preventers stop contaminated water from reversing
direction into the clean water supply, protecting public health.
4. In plumbing systems, what is the purpose of a vent pipe?
A. To drain wastewater
B. To supply hot water
C. To filter contaminants
D. To equalize pressure in the drainage system
Vent pipes allow air into the system, preventing vacuum formation
and ensuring proper drainage flow.
,5. What material is commonly used for residential potable water supply
lines due to its flexibility and corrosion resistance?
A. Cast iron
B. Galvanized steel
C. PEX tubing
D. Clay pipe
PEX tubing is widely used because it resists corrosion, is flexible, and
simplifies installation.
6. Which fixture requires a trap seal primer in certain installations?
A. Kitchen sink
B. Bathtub
C. Floor drain
D. Toilet
Floor drains may dry out over time, so a trap primer maintains the
water seal to prevent sewer gases from entering.
7. What is the primary function of a cleanout in a plumbing system?
A. To supply fresh water
B. To vent gases
C. To allow access for cleaning blockages
D. To regulate pressure
Cleanouts provide access points for removing obstructions and
maintaining drainage systems.
, 8. Which pipe material is most commonly used for underground sanitary
sewer lines?
A. Copper
B. PVC
C. Cast iron or PVC
D. Steel
Both cast iron and PVC are commonly used due to durability and
resistance to corrosion in underground environments.
9. What is the standard test used to check for leaks in a newly installed
drainage system?
A. Air pressure test
B. Water (hydrostatic) test
C. Vacuum test
D. Smoke test
A hydrostatic test fills the system with water to check for leaks under
pressure, ensuring system integrity.
10. What is the main purpose of an air gap in plumbing systems?
A. Increase water pressure
B. Improve drainage
C. Prevent backflow contamination
D. Reduce noise
An air gap provides a physical separation between potable water
and potential contaminants, eliminating backflow risk.
Exam Practice Questions And Correct
Answers (Verified Answers) Plus Rationale
2026 Q&A| Instant Download Pdf
1. During a plumbing inspection, which component is primarily
responsible for preventing sewer gases from entering a building
through fixtures?
A. Vent stack
B. Cleanout
C. Trap
D. Backflow preventer
The trap holds a water seal that blocks sewer gases from traveling
back into occupied spaces, making it essential for sanitation and
safety.
,2. What is the minimum slope generally required for horizontal drainage
piping of 3 inches in diameter or less?
A. 1/16 inch per foot
B. 1/4 inch per foot
C. 1/2 inch per foot
D. 1 inch per foot
A slope of 1/4 inch per foot ensures proper flow velocity to prevent
blockages without causing solids to separate from liquids.
3. Which device is required to protect potable water systems from
contamination due to backflow?
A. Pressure regulator
B. Expansion tank
C. Backflow preventer
D. Air chamber
Backflow preventers stop contaminated water from reversing
direction into the clean water supply, protecting public health.
4. In plumbing systems, what is the purpose of a vent pipe?
A. To drain wastewater
B. To supply hot water
C. To filter contaminants
D. To equalize pressure in the drainage system
Vent pipes allow air into the system, preventing vacuum formation
and ensuring proper drainage flow.
,5. What material is commonly used for residential potable water supply
lines due to its flexibility and corrosion resistance?
A. Cast iron
B. Galvanized steel
C. PEX tubing
D. Clay pipe
PEX tubing is widely used because it resists corrosion, is flexible, and
simplifies installation.
6. Which fixture requires a trap seal primer in certain installations?
A. Kitchen sink
B. Bathtub
C. Floor drain
D. Toilet
Floor drains may dry out over time, so a trap primer maintains the
water seal to prevent sewer gases from entering.
7. What is the primary function of a cleanout in a plumbing system?
A. To supply fresh water
B. To vent gases
C. To allow access for cleaning blockages
D. To regulate pressure
Cleanouts provide access points for removing obstructions and
maintaining drainage systems.
, 8. Which pipe material is most commonly used for underground sanitary
sewer lines?
A. Copper
B. PVC
C. Cast iron or PVC
D. Steel
Both cast iron and PVC are commonly used due to durability and
resistance to corrosion in underground environments.
9. What is the standard test used to check for leaks in a newly installed
drainage system?
A. Air pressure test
B. Water (hydrostatic) test
C. Vacuum test
D. Smoke test
A hydrostatic test fills the system with water to check for leaks under
pressure, ensuring system integrity.
10. What is the main purpose of an air gap in plumbing systems?
A. Increase water pressure
B. Improve drainage
C. Prevent backflow contamination
D. Reduce noise
An air gap provides a physical separation between potable water
and potential contaminants, eliminating backflow risk.
