Master Plumber Licensing Examination
Comprehensive Certification Assessment
1. Which of the following is the minimum pipe size allowed for a
water closet (toilet) drain according to standard plumbing codes?
A. 2 inches
B. 3 inches
C. 4 inches
D. 1.5 inches
Rationale: The standard plumbing codes require a minimum 3-inch
diameter drain for water closets to ensure proper flow and prevent
clogging.
2. What is the purpose of a trap in a plumbing system?
A. To increase water pressure
B. To prevent sewer gases from entering the building
C. To filter water
D. To reduce water velocity
Rationale: A trap holds water that acts as a barrier to prevent sewer
gases from coming back into the building.
3. Which of the following is a standard slope for horizontal drainage
piping?
,A. 1/2 inch per foot
B. 1/16 inch per foot
C. 1/4 inch per foot
D. 1 inch per foot
Rationale: Horizontal drainage pipes should have a minimum slope of
1/4 inch per foot to ensure proper flow without causing excessive
turbulence or backups.
4. Which type of valve is commonly used to shut off water supply to a
fixture?
A. Ball check valve
B. Pressure reducing valve
C. Angle stop valve
D. Gate valve
Rationale: An angle stop valve is typically installed under sinks and
toilets to allow isolation of the fixture without shutting off the entire
water supply.
5. What is the maximum allowable water velocity in a residential
water supply pipe to prevent pipe noise and erosion?
A. 5 feet per second
B. 8 feet per second
C. 12 feet per second
D. 15 feet per second
Rationale: Residential plumbing codes generally limit water velocity
,to 8 feet per second in supply pipes to prevent water hammer, noise,
and pipe wear.
6. What is the purpose of venting in a plumbing system?
A. To filter water
B. To heat water
C. To allow air to enter the drainage system and prevent siphoning of
traps
D. To pressurize the water system
Rationale: Venting maintains atmospheric pressure in drain pipes and
prevents traps from being siphoned, which keeps sewer gases out.
7. Which material is most commonly used for underground water
service lines?
A. PVC
B. Copper or PEX
C. Cast iron
D. ABS
Rationale: Copper and PEX are commonly approved for underground
potable water service lines because they are durable and resistant to
corrosion.
8. How often must backflow prevention devices be tested according
to standard plumbing codes?
, A. Monthly
B. Annually
C. Every 5 years
D. Only upon installation
Rationale: Most plumbing codes require annual testing of backflow
prevention devices to ensure they function properly and protect
potable water.
9. Which of the following is an approved method for joining copper
tubing?
A. Solvent cement
B. Mechanical threading only
C. Soldering, compression, and press fittings
D. Welding
Rationale: Copper tubing can be joined using soldering (sweat),
compression, and press fittings; solvent cement is used for plastics,
not copper.
10. What is the minimum air gap required between a potable water
outlet and the flood level of a fixture?
A. 1 inch
B. 2 inches
C. 3 inches
D. 4 inches
Rationale: Plumbing codes generally require a minimum 2-inch air gap
to prevent backflow and contamination of potable water.
Comprehensive Certification Assessment
1. Which of the following is the minimum pipe size allowed for a
water closet (toilet) drain according to standard plumbing codes?
A. 2 inches
B. 3 inches
C. 4 inches
D. 1.5 inches
Rationale: The standard plumbing codes require a minimum 3-inch
diameter drain for water closets to ensure proper flow and prevent
clogging.
2. What is the purpose of a trap in a plumbing system?
A. To increase water pressure
B. To prevent sewer gases from entering the building
C. To filter water
D. To reduce water velocity
Rationale: A trap holds water that acts as a barrier to prevent sewer
gases from coming back into the building.
3. Which of the following is a standard slope for horizontal drainage
piping?
,A. 1/2 inch per foot
B. 1/16 inch per foot
C. 1/4 inch per foot
D. 1 inch per foot
Rationale: Horizontal drainage pipes should have a minimum slope of
1/4 inch per foot to ensure proper flow without causing excessive
turbulence or backups.
4. Which type of valve is commonly used to shut off water supply to a
fixture?
A. Ball check valve
B. Pressure reducing valve
C. Angle stop valve
D. Gate valve
Rationale: An angle stop valve is typically installed under sinks and
toilets to allow isolation of the fixture without shutting off the entire
water supply.
5. What is the maximum allowable water velocity in a residential
water supply pipe to prevent pipe noise and erosion?
A. 5 feet per second
B. 8 feet per second
C. 12 feet per second
D. 15 feet per second
Rationale: Residential plumbing codes generally limit water velocity
,to 8 feet per second in supply pipes to prevent water hammer, noise,
and pipe wear.
6. What is the purpose of venting in a plumbing system?
A. To filter water
B. To heat water
C. To allow air to enter the drainage system and prevent siphoning of
traps
D. To pressurize the water system
Rationale: Venting maintains atmospheric pressure in drain pipes and
prevents traps from being siphoned, which keeps sewer gases out.
7. Which material is most commonly used for underground water
service lines?
A. PVC
B. Copper or PEX
C. Cast iron
D. ABS
Rationale: Copper and PEX are commonly approved for underground
potable water service lines because they are durable and resistant to
corrosion.
8. How often must backflow prevention devices be tested according
to standard plumbing codes?
, A. Monthly
B. Annually
C. Every 5 years
D. Only upon installation
Rationale: Most plumbing codes require annual testing of backflow
prevention devices to ensure they function properly and protect
potable water.
9. Which of the following is an approved method for joining copper
tubing?
A. Solvent cement
B. Mechanical threading only
C. Soldering, compression, and press fittings
D. Welding
Rationale: Copper tubing can be joined using soldering (sweat),
compression, and press fittings; solvent cement is used for plastics,
not copper.
10. What is the minimum air gap required between a potable water
outlet and the flood level of a fixture?
A. 1 inch
B. 2 inches
C. 3 inches
D. 4 inches
Rationale: Plumbing codes generally require a minimum 2-inch air gap
to prevent backflow and contamination of potable water.
