TEXAS MASTER PLUMBER EXAM
1. What is the minimum size of a water service pipe for a
single-family dwelling in most code applications?
A. 1/2 inch
B. 3/4 inch
C. 1 inch
D. 1 1/2 inch
Correct answer: B. 3/4 inch
Rationale: Most plumbing codes require a minimum 3/4-inch
water service for single-family dwellings to ensure adequate
flow and pressure under peak demand conditions. Smaller sizes
may lead to excessive friction loss and insufficient fixture
supply.
2. What is the primary purpose of a P-trap in a plumbing
system?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Filter solid waste
D. Control water temperature
Correct answer: B. Prevent sewer gases from entering the
building
Rationale: A P-trap retains a water seal that blocks sewer gases
from backing up into occupied spaces while still allowing
wastewater to flow freely.
, 3. Which of the following is the most common material used
for residential water distribution piping today?
A. Cast iron
B. Galvanized steel
C. Copper or PEX
D. Lead
Correct answer: C. Copper or PEX
Rationale: Copper and PEX are widely used due to corrosion
resistance, durability, and ease of installation compared to
older materials like galvanized steel or lead.
4. What is the minimum slope required 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
Correct answer: A. 1/8 inch per foot
Rationale: Larger drain pipes (3 inches or more) typically require
a minimum slope of 1/8 inch per foot to maintain proper flow
velocity without causing solids separation.
5. What device is used to prevent backflow in a potable
water system?
A. Pressure regulator
B. Check valve or backflow preventer
C. Air chamber
D. Gate valve
,Correct answer: B. Check valve or backflow preventer
Rationale: Backflow preventers stop contaminated water from
reversing flow direction into potable water supplies, protecting
public health.
6. What is the function of a cleanout in a drainage system?
A. Increase flow speed
B. Provide access for clearing blockages
C. Vent sewer gases
D. Trap debris
Correct answer: B. Provide access for clearing blockages
Rationale: Cleanouts allow plumbers to access drain lines for
inspection and removal of obstructions without dismantling
piping.
7. Which pipe material is prohibited for new potable water
systems in modern codes?
A. Copper
B. PEX
C. Lead
D. PVC
Correct answer: C. Lead
Rationale: Lead piping is banned due to its toxicity and ability to
leach harmful contaminants into drinking water.
8. What is the purpose of a vent system in plumbing?
A. Increase water flow
B. Allow sewer gases to escape and maintain trap seals
, C. Heat water
D. Filter wastewater
Correct answer: B. Allow sewer gases to escape and maintain
trap seals
Rationale: Venting prevents pressure imbalances that could
siphon water from traps, maintaining proper barrier against
sewer gases.
9. What is the standard test pressure for water supply piping
in many plumbing codes?
A. 25 psi
B. 50 psi
C. 100 psi
D. 200 psi
Correct answer: C. 100 psi
Rationale: Water supply systems are commonly tested at 100
psi to verify integrity and detect leaks before commissioning.
10. Which fixture requires a dedicated vent in most
plumbing codes?
A. Hose bibb
B. Toilet
C. Floor drain
D. Shower only
Correct answer: B. Toilet
Rationale: Toilets require proper venting to ensure efficient
flushing and prevent siphonage of trap seals.
1. What is the minimum size of a water service pipe for a
single-family dwelling in most code applications?
A. 1/2 inch
B. 3/4 inch
C. 1 inch
D. 1 1/2 inch
Correct answer: B. 3/4 inch
Rationale: Most plumbing codes require a minimum 3/4-inch
water service for single-family dwellings to ensure adequate
flow and pressure under peak demand conditions. Smaller sizes
may lead to excessive friction loss and insufficient fixture
supply.
2. What is the primary purpose of a P-trap in a plumbing
system?
A. Increase water pressure
B. Prevent sewer gases from entering the building
C. Filter solid waste
D. Control water temperature
Correct answer: B. Prevent sewer gases from entering the
building
Rationale: A P-trap retains a water seal that blocks sewer gases
from backing up into occupied spaces while still allowing
wastewater to flow freely.
, 3. Which of the following is the most common material used
for residential water distribution piping today?
A. Cast iron
B. Galvanized steel
C. Copper or PEX
D. Lead
Correct answer: C. Copper or PEX
Rationale: Copper and PEX are widely used due to corrosion
resistance, durability, and ease of installation compared to
older materials like galvanized steel or lead.
4. What is the minimum slope required 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
Correct answer: A. 1/8 inch per foot
Rationale: Larger drain pipes (3 inches or more) typically require
a minimum slope of 1/8 inch per foot to maintain proper flow
velocity without causing solids separation.
5. What device is used to prevent backflow in a potable
water system?
A. Pressure regulator
B. Check valve or backflow preventer
C. Air chamber
D. Gate valve
,Correct answer: B. Check valve or backflow preventer
Rationale: Backflow preventers stop contaminated water from
reversing flow direction into potable water supplies, protecting
public health.
6. What is the function of a cleanout in a drainage system?
A. Increase flow speed
B. Provide access for clearing blockages
C. Vent sewer gases
D. Trap debris
Correct answer: B. Provide access for clearing blockages
Rationale: Cleanouts allow plumbers to access drain lines for
inspection and removal of obstructions without dismantling
piping.
7. Which pipe material is prohibited for new potable water
systems in modern codes?
A. Copper
B. PEX
C. Lead
D. PVC
Correct answer: C. Lead
Rationale: Lead piping is banned due to its toxicity and ability to
leach harmful contaminants into drinking water.
8. What is the purpose of a vent system in plumbing?
A. Increase water flow
B. Allow sewer gases to escape and maintain trap seals
, C. Heat water
D. Filter wastewater
Correct answer: B. Allow sewer gases to escape and maintain
trap seals
Rationale: Venting prevents pressure imbalances that could
siphon water from traps, maintaining proper barrier against
sewer gases.
9. What is the standard test pressure for water supply piping
in many plumbing codes?
A. 25 psi
B. 50 psi
C. 100 psi
D. 200 psi
Correct answer: C. 100 psi
Rationale: Water supply systems are commonly tested at 100
psi to verify integrity and detect leaks before commissioning.
10. Which fixture requires a dedicated vent in most
plumbing codes?
A. Hose bibb
B. Toilet
C. Floor drain
D. Shower only
Correct answer: B. Toilet
Rationale: Toilets require proper venting to ensure efficient
flushing and prevent siphonage of trap seals.
