NYC Master Plumber License
Examination: 100 Comprehensive
Practice Questions, Verified Answers &
Detailed Rationales (2026 Edition)
1. What is the minimum required slope for a horizontal drainage pipe 3 inches
in diameter or less under NYC Plumbing Code?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Rationale: Proper slope ensures adequate velocity for waste transport and
prevents solids from settling in small-diameter drainage piping.
2. The primary purpose of a trap in a plumbing system is to:
A. Increase flow velocity
B. Prevent backflow only
C. Prevent sewer gases from entering the building
D. Increase pipe pressure
Rationale: Traps retain a water seal that blocks sewer gases while
allowing wastewater to pass.
3. What is the minimum water seal depth for a standard P-trap?
A. 1 inch
B. 2 inches
, C. 3 inches
D. 4 inches
Rationale: A 2-inch seal is standard to prevent siphonage and evaporation
loss.
4. Vent piping is installed primarily to:
A. Increase water pressure
B. Drain storm water
C. Maintain neutral air pressure in drainage systems
D. Increase pipe diameter
Rationale: Venting prevents trap siphonage and allows proper system
airflow.
5. A backwater valve is installed to:
A. Increase flow rate
B. Prevent sewage backup into a building
C. Increase pipe pressure
D. Filter solids
Rationale: Backwater valves close automatically to prevent reverse flow
during sewer surcharge.
6. Which material is commonly approved for underground drainage piping in
NYC?
A. Galvanized steel
B. Copper
C. PVC (Schedule 40 or approved equivalent)
D. Aluminum
Rationale: PVC is corrosion-resistant and commonly used for underground
drainage.
7. The minimum size for a building sewer connection in most NYC applications
is:
A. 2 inches
B. 3 inches
C. 4 inches
, D. 6 inches
Rationale: 4-inch minimum ensures adequate capacity for building
discharge.
8. A cleanout must be installed:
A. Only at roof level
B. At intervals and changes of direction in drainage piping
C. Only at fixtures
D. Only underground
Rationale: Cleanouts allow access for maintenance and clearing
blockages.
9. The maximum distance between vent connections is governed by:
A. Pipe color
B. Fixture height
C. Plumbing code and trap arm length limits
D. Water pressure
Rationale: Vent spacing ensures trap protection and system balance.
10.Which fixture requires a separate vent in most cases?
A. Floor drain
B. Hose bibb
C. Toilet (water closet)
D. Roof drain
Rationale: Toilets require proper venting due to high discharge volume.
11.The purpose of a fixture trap arm is to:
A. Increase water velocity
B. Connect trap to vent system within allowable distance
C. Store wastewater
D. Increase pressure
Rationale: The trap arm must maintain proper slope and vent connection.
12.A stack vent extends:
A. To the basement
Examination: 100 Comprehensive
Practice Questions, Verified Answers &
Detailed Rationales (2026 Edition)
1. What is the minimum required slope for a horizontal drainage pipe 3 inches
in diameter or less under NYC Plumbing Code?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Rationale: Proper slope ensures adequate velocity for waste transport and
prevents solids from settling in small-diameter drainage piping.
2. The primary purpose of a trap in a plumbing system is to:
A. Increase flow velocity
B. Prevent backflow only
C. Prevent sewer gases from entering the building
D. Increase pipe pressure
Rationale: Traps retain a water seal that blocks sewer gases while
allowing wastewater to pass.
3. What is the minimum water seal depth for a standard P-trap?
A. 1 inch
B. 2 inches
, C. 3 inches
D. 4 inches
Rationale: A 2-inch seal is standard to prevent siphonage and evaporation
loss.
4. Vent piping is installed primarily to:
A. Increase water pressure
B. Drain storm water
C. Maintain neutral air pressure in drainage systems
D. Increase pipe diameter
Rationale: Venting prevents trap siphonage and allows proper system
airflow.
5. A backwater valve is installed to:
A. Increase flow rate
B. Prevent sewage backup into a building
C. Increase pipe pressure
D. Filter solids
Rationale: Backwater valves close automatically to prevent reverse flow
during sewer surcharge.
6. Which material is commonly approved for underground drainage piping in
NYC?
A. Galvanized steel
B. Copper
C. PVC (Schedule 40 or approved equivalent)
D. Aluminum
Rationale: PVC is corrosion-resistant and commonly used for underground
drainage.
7. The minimum size for a building sewer connection in most NYC applications
is:
A. 2 inches
B. 3 inches
C. 4 inches
, D. 6 inches
Rationale: 4-inch minimum ensures adequate capacity for building
discharge.
8. A cleanout must be installed:
A. Only at roof level
B. At intervals and changes of direction in drainage piping
C. Only at fixtures
D. Only underground
Rationale: Cleanouts allow access for maintenance and clearing
blockages.
9. The maximum distance between vent connections is governed by:
A. Pipe color
B. Fixture height
C. Plumbing code and trap arm length limits
D. Water pressure
Rationale: Vent spacing ensures trap protection and system balance.
10.Which fixture requires a separate vent in most cases?
A. Floor drain
B. Hose bibb
C. Toilet (water closet)
D. Roof drain
Rationale: Toilets require proper venting due to high discharge volume.
11.The purpose of a fixture trap arm is to:
A. Increase water velocity
B. Connect trap to vent system within allowable distance
C. Store wastewater
D. Increase pressure
Rationale: The trap arm must maintain proper slope and vent connection.
12.A stack vent extends:
A. To the basement
