Missouri Plumbing Contractor License
— Springfield Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. What is the minimum size vent required for a single bathroom group
under most plumbing codes?
A) 1/2 inch
B) 3/4 inch
C) 1 1/4 inch
D) 2 inch
C) 1 1/4 inch
Rationale: A 1 1/4 inch vent is commonly the minimum size to
prevent trap seal loss and ensure proper air circulation.
2. The primary purpose of a plumbing trap is to:
A) Increase water pressure
B) Prevent sewer gases from entering the building
, C) Speed up drainage
D) Filter solids
B) Prevent sewer gases from entering the building
Rationale: Traps retain a water seal that blocks sewer gases from
entering occupied spaces.
3. Which pipe material is most commonly used for DWV systems in
modern residential construction?
A) Cast iron
B) Galvanized steel
C) PVC
D) Lead
C) PVC
Rationale: PVC is lightweight, corrosion-resistant, and widely used
for drainage systems.
4. What is the minimum slope for a 3-inch horizontal drain 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
Rationale: A 1/4 inch per foot slope ensures proper gravity flow and
prevents solids buildup.
,5. A backflow preventer is used to:
A) Increase flow rate
B) Prevent reverse flow of contaminated water
C) Reduce pipe noise
D) Increase pipe pressure
B) Prevent reverse flow of contaminated water
Rationale: Backflow devices protect potable water from
contamination.
6. What is the function of a cleanout in a drainage system?
A) Increase venting
B) Provide access for removing blockages
C) Regulate water pressure
D) Filter wastewater
B) Provide access for removing blockages
Rationale: Cleanouts allow maintenance access to drain lines.
7. Which fitting is used to change pipe direction 90 degrees with minimal
resistance?
A) Tee
B) Elbow
C) Wye
D) Coupling
B) Elbow
Rationale: Elbows provide directional changes in piping systems.
, 8. What type of vent prevents pressure buildup in drainage systems?
A) Loop vent
B) Stack vent
C) Air admittance valve
D) All of the above
D) All of the above
Rationale: All listed vents help regulate air pressure in DWV systems.
9. The main water shutoff valve is typically located:
A) At the water heater
B) At each fixture
C) Where the water service enters the building
D) In the attic
C) Where the water service enters the building
Rationale: This allows control of the entire water supply.
10. What is the purpose of pipe reaming?
A) Cutting pipe
B) Removing burrs after cutting
C) Painting pipe
D) Thread sealing
B) Removing burrs after cutting
Rationale: Reaming ensures smooth flow and prevents turbulence.
11. Which is a venting method where multiple fixtures connect to a
single vent stack?
— Springfield Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the minimum size vent required for a single bathroom group
under most plumbing codes?
A) 1/2 inch
B) 3/4 inch
C) 1 1/4 inch
D) 2 inch
C) 1 1/4 inch
Rationale: A 1 1/4 inch vent is commonly the minimum size to
prevent trap seal loss and ensure proper air circulation.
2. The primary purpose of a plumbing trap is to:
A) Increase water pressure
B) Prevent sewer gases from entering the building
, C) Speed up drainage
D) Filter solids
B) Prevent sewer gases from entering the building
Rationale: Traps retain a water seal that blocks sewer gases from
entering occupied spaces.
3. Which pipe material is most commonly used for DWV systems in
modern residential construction?
A) Cast iron
B) Galvanized steel
C) PVC
D) Lead
C) PVC
Rationale: PVC is lightweight, corrosion-resistant, and widely used
for drainage systems.
4. What is the minimum slope for a 3-inch horizontal drain 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
Rationale: A 1/4 inch per foot slope ensures proper gravity flow and
prevents solids buildup.
,5. A backflow preventer is used to:
A) Increase flow rate
B) Prevent reverse flow of contaminated water
C) Reduce pipe noise
D) Increase pipe pressure
B) Prevent reverse flow of contaminated water
Rationale: Backflow devices protect potable water from
contamination.
6. What is the function of a cleanout in a drainage system?
A) Increase venting
B) Provide access for removing blockages
C) Regulate water pressure
D) Filter wastewater
B) Provide access for removing blockages
Rationale: Cleanouts allow maintenance access to drain lines.
7. Which fitting is used to change pipe direction 90 degrees with minimal
resistance?
A) Tee
B) Elbow
C) Wye
D) Coupling
B) Elbow
Rationale: Elbows provide directional changes in piping systems.
, 8. What type of vent prevents pressure buildup in drainage systems?
A) Loop vent
B) Stack vent
C) Air admittance valve
D) All of the above
D) All of the above
Rationale: All listed vents help regulate air pressure in DWV systems.
9. The main water shutoff valve is typically located:
A) At the water heater
B) At each fixture
C) Where the water service enters the building
D) In the attic
C) Where the water service enters the building
Rationale: This allows control of the entire water supply.
10. What is the purpose of pipe reaming?
A) Cutting pipe
B) Removing burrs after cutting
C) Painting pipe
D) Thread sealing
B) Removing burrs after cutting
Rationale: Reaming ensures smooth flow and prevents turbulence.
11. Which is a venting method where multiple fixtures connect to a
single vent stack?
