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Colorado Residential Plumber License
Examination Practice Exam 2026 | 100
Questions & Answers with Detailed
Rationales | Complete Colorado
Residential Plumber Exam Prep & Study
Guide
1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent sewer gases from entering the building
C. To increase drainage velocity
D. To provide additional cleanout access
Answer: To prevent sewer gases from entering the building
Rationale: A properly installed trap maintains a water seal that prevents sewer
gases and odors from entering occupied spaces while allowing wastewater to
drain.
2. Which plumbing code is specifically identified by Colorado as part of the
adopted Colorado Plumbing Code?
A. National Electrical Code
B. International Plumbing Code
,C. Uniform Mechanical Code only
D. National Fuel Gas Code only
Answer: International Plumbing Code
Rationale: Colorado's Plumbing Board incorporates specified editions and
provisions of the International Plumbing Code and International Residential
Code into the Colorado Plumbing Code.
3. What is the minimum practical experience listed by Colorado for a
residential plumber applicant?
A. 1,700 hours
B. 2,500 hours
C. 3,400 hours
D. 6,800 hours
Answer: 3,400 hours
Rationale: Colorado lists two years, or 3,400 hours, of practical experience for
residential plumber applicants.
4. What is the primary purpose of a cleanout?
A. To increase water pressure
B. To provide access for cleaning and removing obstructions
C. To prevent freezing
D. To replace a trap
Answer: To provide access for cleaning and removing obstructions
Rationale: Cleanouts provide accessible openings in drainage piping so that
blockages can be located and removed.
5. What type of fitting should generally be used to join horizontal drainage
piping to a vertical drain?
,A. Straight coupling
B. Sanitary tee
C. Reducing coupling
D. Union
Answer: Sanitary tee
Rationale: A sanitary tee is commonly used for connecting a horizontal branch
to a vertical drainage stack in the proper direction of flow. Its use is subject to
the specific drainage arrangement and code requirements.
6. What is the purpose of a venting system in a drainage installation?
A. To supply drinking water
B. To protect trap seals and allow proper drainage-system airflow
C. To increase water temperature
D. To reduce pipe diameter
Answer: To protect trap seals and allow proper drainage-system airflow
Rationale: Drainage vents equalize pressure and help prevent siphonage or
backpressure that could destroy trap seals.
7. What condition can cause a trap to lose its water seal through siphonage?
A. Excessive pipe insulation
B. Negative pressure in the drainage system
C. Low water temperature
D. Oversized supply piping
Answer: Negative pressure in the drainage system
Rationale: Negative pressure can siphon water out of a trap, exposing the
building to sewer gases.
8. What is backflow?
, A. Forward flow in a drain
B. Reversal of normal flow direction
C. Expansion of hot water
D. Water hammer
Answer: Reversal of normal flow direction
Rationale: Backflow occurs when water or another substance flows in the
opposite direction from the intended direction.
9. What is backpressure backflow?
A. Backflow caused by a higher downstream pressure
B. Backflow caused only by gravity
C. Backflow caused by a broken trap
D. Backflow caused by low water temperature
Answer: Backflow caused by a higher downstream pressure
Rationale: Backpressure occurs when the pressure downstream of a potable-
water connection becomes greater than the supply pressure, potentially forcing
contaminants backward.
10.What is backsiphonage?
A. Backflow caused by negative pressure in the supply system
B. Backflow caused by excessive drainage slope
C. Drainage caused by a blocked vent
D. Water hammer caused by a valve
Answer: Backflow caused by negative pressure in the supply system
Rationale: Backsiphonage can occur when a vacuum or negative pressure
develops in the potable-water supply, drawing nonpotable water backward.
11.What device is commonly used to prevent backsiphonage at a hose
connection?
Colorado Residential Plumber License
Examination Practice Exam 2026 | 100
Questions & Answers with Detailed
Rationales | Complete Colorado
Residential Plumber Exam Prep & Study
Guide
1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent sewer gases from entering the building
C. To increase drainage velocity
D. To provide additional cleanout access
Answer: To prevent sewer gases from entering the building
Rationale: A properly installed trap maintains a water seal that prevents sewer
gases and odors from entering occupied spaces while allowing wastewater to
drain.
2. Which plumbing code is specifically identified by Colorado as part of the
adopted Colorado Plumbing Code?
A. National Electrical Code
B. International Plumbing Code
,C. Uniform Mechanical Code only
D. National Fuel Gas Code only
Answer: International Plumbing Code
Rationale: Colorado's Plumbing Board incorporates specified editions and
provisions of the International Plumbing Code and International Residential
Code into the Colorado Plumbing Code.
3. What is the minimum practical experience listed by Colorado for a
residential plumber applicant?
A. 1,700 hours
B. 2,500 hours
C. 3,400 hours
D. 6,800 hours
Answer: 3,400 hours
Rationale: Colorado lists two years, or 3,400 hours, of practical experience for
residential plumber applicants.
4. What is the primary purpose of a cleanout?
A. To increase water pressure
B. To provide access for cleaning and removing obstructions
C. To prevent freezing
D. To replace a trap
Answer: To provide access for cleaning and removing obstructions
Rationale: Cleanouts provide accessible openings in drainage piping so that
blockages can be located and removed.
5. What type of fitting should generally be used to join horizontal drainage
piping to a vertical drain?
,A. Straight coupling
B. Sanitary tee
C. Reducing coupling
D. Union
Answer: Sanitary tee
Rationale: A sanitary tee is commonly used for connecting a horizontal branch
to a vertical drainage stack in the proper direction of flow. Its use is subject to
the specific drainage arrangement and code requirements.
6. What is the purpose of a venting system in a drainage installation?
A. To supply drinking water
B. To protect trap seals and allow proper drainage-system airflow
C. To increase water temperature
D. To reduce pipe diameter
Answer: To protect trap seals and allow proper drainage-system airflow
Rationale: Drainage vents equalize pressure and help prevent siphonage or
backpressure that could destroy trap seals.
7. What condition can cause a trap to lose its water seal through siphonage?
A. Excessive pipe insulation
B. Negative pressure in the drainage system
C. Low water temperature
D. Oversized supply piping
Answer: Negative pressure in the drainage system
Rationale: Negative pressure can siphon water out of a trap, exposing the
building to sewer gases.
8. What is backflow?
, A. Forward flow in a drain
B. Reversal of normal flow direction
C. Expansion of hot water
D. Water hammer
Answer: Reversal of normal flow direction
Rationale: Backflow occurs when water or another substance flows in the
opposite direction from the intended direction.
9. What is backpressure backflow?
A. Backflow caused by a higher downstream pressure
B. Backflow caused only by gravity
C. Backflow caused by a broken trap
D. Backflow caused by low water temperature
Answer: Backflow caused by a higher downstream pressure
Rationale: Backpressure occurs when the pressure downstream of a potable-
water connection becomes greater than the supply pressure, potentially forcing
contaminants backward.
10.What is backsiphonage?
A. Backflow caused by negative pressure in the supply system
B. Backflow caused by excessive drainage slope
C. Drainage caused by a blocked vent
D. Water hammer caused by a valve
Answer: Backflow caused by negative pressure in the supply system
Rationale: Backsiphonage can occur when a vacuum or negative pressure
develops in the potable-water supply, drawing nonpotable water backward.
11.What device is commonly used to prevent backsiphonage at a hose
connection?
