Minnesota Master Plumber Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of a plumbing vent
system?
A) Increase water pressure in fixtures
B) Prevent sewer gases from entering the building and maintain trap
seals
C) Speed up wastewater flow in drain lines
D) Eliminate the need for traps
B) Prevent sewer gases from entering the building and maintain trap
seals
The vent system equalizes air pressure within the drainage system,
protecting trap seals from siphonage or backpressure while
preventing harmful sewer gases from entering occupied spaces.
2. What is the minimum slope required for a 3-inch horizontal drain line
under most plumbing codes?
, A) 1/16 inch per foot
B) 1/8 inch per foot
C) 1/4 inch per foot
D) 1/2 inch per foot
C) 1/4 inch per foot
Standard plumbing codes generally require a 1/4-inch per foot slope
for 3-inch and smaller drainage piping to ensure adequate flow
velocity and prevent solids from settling.
3. Which device is designed to prevent backflow in a potable water
system?
A) Trap primer
B) Backwater valve
C) Backflow preventer
D) Cleanout
C) Backflow preventer
Backflow preventers protect potable water systems from
contamination by stopping reverse flow caused by backpressure or
backsiphonage.
4. What is the function of a P-trap?
A) Increase water flow velocity
B) Store wastewater temporarily
C) Prevent sewer gases from entering the building
D) Filter solid waste
, C) Prevent sewer gases from entering the building
A P-trap maintains a water seal that blocks sewer gases while
allowing wastewater to pass through the drainage system.
5. Which material is most commonly used for underground water service
piping?
A) Copper Type M
B) Galvanized steel
C) PEX SDR-rated tubing
D) PVC DWV
C) PEX SDR-rated tubing
PEX tubing is widely used for underground water service due to its
flexibility, corrosion resistance, and ease of installation.
6. What is the minimum size of a building sewer serving a single-family
dwelling under most codes?
A) 2 inches
B) 3 inches
C) 4 inches
D) 6 inches
C) 4 inches
A 4-inch building sewer is typically the minimum size to ensure
adequate capacity and prevent blockages in residential systems.
7. What is the primary purpose of a cleanout in a drainage system?
A) Increase drainage speed
, B) Provide access for clearing blockages
C) Vent sewer gases
D) Reduce pipe pressure
B) Provide access for clearing blockages
Cleanouts allow plumbers to access drainage systems for inspection
and removal of obstructions.
8. Which fixture unit measurement is used primarily for plumbing system
sizing?
A) Gallons per minute
B) Fixture Units
C) PSI
D) BTU
B) Fixture Units
Fixture units quantify the load on a plumbing system, helping
designers size pipes accurately based on expected demand.
9. What is the minimum air gap required for potable water protection in
most codes?
A) 1/4 inch
B) 1 inch
C) Twice the pipe diameter
D) Equal to pipe diameter
B) 1 inch
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of a plumbing vent
system?
A) Increase water pressure in fixtures
B) Prevent sewer gases from entering the building and maintain trap
seals
C) Speed up wastewater flow in drain lines
D) Eliminate the need for traps
B) Prevent sewer gases from entering the building and maintain trap
seals
The vent system equalizes air pressure within the drainage system,
protecting trap seals from siphonage or backpressure while
preventing harmful sewer gases from entering occupied spaces.
2. What is the minimum slope required for a 3-inch horizontal drain line
under most plumbing codes?
, A) 1/16 inch per foot
B) 1/8 inch per foot
C) 1/4 inch per foot
D) 1/2 inch per foot
C) 1/4 inch per foot
Standard plumbing codes generally require a 1/4-inch per foot slope
for 3-inch and smaller drainage piping to ensure adequate flow
velocity and prevent solids from settling.
3. Which device is designed to prevent backflow in a potable water
system?
A) Trap primer
B) Backwater valve
C) Backflow preventer
D) Cleanout
C) Backflow preventer
Backflow preventers protect potable water systems from
contamination by stopping reverse flow caused by backpressure or
backsiphonage.
4. What is the function of a P-trap?
A) Increase water flow velocity
B) Store wastewater temporarily
C) Prevent sewer gases from entering the building
D) Filter solid waste
, C) Prevent sewer gases from entering the building
A P-trap maintains a water seal that blocks sewer gases while
allowing wastewater to pass through the drainage system.
5. Which material is most commonly used for underground water service
piping?
A) Copper Type M
B) Galvanized steel
C) PEX SDR-rated tubing
D) PVC DWV
C) PEX SDR-rated tubing
PEX tubing is widely used for underground water service due to its
flexibility, corrosion resistance, and ease of installation.
6. What is the minimum size of a building sewer serving a single-family
dwelling under most codes?
A) 2 inches
B) 3 inches
C) 4 inches
D) 6 inches
C) 4 inches
A 4-inch building sewer is typically the minimum size to ensure
adequate capacity and prevent blockages in residential systems.
7. What is the primary purpose of a cleanout in a drainage system?
A) Increase drainage speed
, B) Provide access for clearing blockages
C) Vent sewer gases
D) Reduce pipe pressure
B) Provide access for clearing blockages
Cleanouts allow plumbers to access drainage systems for inspection
and removal of obstructions.
8. Which fixture unit measurement is used primarily for plumbing system
sizing?
A) Gallons per minute
B) Fixture Units
C) PSI
D) BTU
B) Fixture Units
Fixture units quantify the load on a plumbing system, helping
designers size pipes accurately based on expected demand.
9. What is the minimum air gap required for potable water protection in
most codes?
A) 1/4 inch
B) 1 inch
C) Twice the pipe diameter
D) Equal to pipe diameter
B) 1 inch
