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According to the International Plumbing Code (IPC) as adopted by DC, what is the minimum size for a building sewer?

2 inches

3 inches

4 inches

6 inches

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Key Facts: DC Plumber Exam

70%

Passing Score

DCRA

~80

Questions

3-hour limit

~$305

Exam Fee

PSI/DCRA

IPC

Code Base

DCRA adoption

DC's journeyman plumber exam is based on the IPC and administered by PSI under DCRA. The exam has approximately 80 questions with a 3-hour time limit and requires 70% to pass. DC's dense urban environment means emphasis on multi-story plumbing, backflow prevention, and grease interceptor installations.

Sample DC Plumber Practice Questions

Try these sample questions to test your DC Plumber exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1According to the International Plumbing Code (IPC) as adopted by DC, what is the minimum size for a building sewer?

A.2 inches

B.3 inches

C.4 inches

D.6 inches

Explanation: Per IPC Section 703.1, the minimum size of a building sewer is 3 inches in diameter. However, when a water closet is connected, the minimum increases to 3 inches. The building sewer must be properly sized based on total drainage fixture unit (DFU) load.

2Under DCRA regulations, what is the minimum slope required for a 3-inch horizontal drainage pipe?

A.1/16 inch per foot

B.1/8 inch per foot

C.1/4 inch per foot

D.1/2 inch per foot

Explanation: Per IPC Table 704.1, horizontal drainage pipes 3 inches and larger require a minimum slope of 1/8 inch per foot. Pipes smaller than 3 inches require a minimum slope of 1/4 inch per foot. Proper slope ensures adequate flow velocity to carry solids.

3What is the DFU value for a residential water closet (1.6 gpf) under the IPC?

A.2 DFU

B.3 DFU

C.4 DFU

D.6 DFU

Explanation: Per IPC Table 709.1, a residential water closet with a flush volume of 1.6 gallons per flush is assigned a value of 3 drainage fixture units (DFU). This value is used for sizing drainage and vent piping throughout the system.

4What is the maximum distance between cleanouts on a horizontal drainage pipe per the IPC?

A.50 feet

B.75 feet

C.100 feet

D.150 feet

Explanation: Per IPC Section 708.3.5, cleanouts must be installed at intervals not exceeding 100 feet on horizontal drainage lines. This spacing ensures that the entire drainage system can be effectively maintained and cleared of blockages.

5In DC, what type of backflow preventer is required for a high-hazard cross-connection?

A.Atmospheric vacuum breaker (AVB)

B.Pressure vacuum breaker (PVB)

C.Double check valve assembly (DCVA)

D.Reduced pressure zone (RPZ) assembly

Explanation: Per IPC Section 608.16, a reduced pressure zone (RPZ) backflow preventer is required for high-hazard cross-connections where the potential contaminant could cause a health hazard. The RPZ provides the highest level of backflow protection with a relief valve between two check valves.

6What is the minimum water supply pipe size for a bathtub with a shower per the IPC?

A.3/8 inch

B.1/2 inch

C.3/4 inch

D.1 inch

Explanation: Per IPC Table 604.5, the minimum supply pipe size for a bathtub with a shower is 1/2 inch. This sizing ensures adequate flow rate and pressure at the fixture. Branch supply lines to bathtub/shower combinations must be at least 1/2 inch.

7What is the maximum water temperature setting for a residential water heater per the IPC?

A.110°F

B.120°F

C.140°F

D.180°F

Explanation: Per IPC Section 607.1, the maximum hot water temperature for residential fixtures is 120°F. Water heaters may be set higher for sanitization purposes, but anti-scald devices or thermostatic mixing valves must limit output to 120°F at fixtures to prevent burns.

8What is the minimum trap seal depth required by the IPC for a standard plumbing fixture trap?

A.1 inch

B.2 inches

C.3 inches

D.4 inches

Explanation: Per IPC Section 1002.1, the minimum trap seal depth is 2 inches and the maximum is 4 inches. The water seal in a trap prevents sewer gases from entering the building through fixture drains. Maintaining proper trap seal depth is essential for health and safety.

9Under the IPC as adopted in DC, what is the minimum vent pipe size for a water closet?

A.1-1/4 inches

B.1-1/2 inches

C.2 inches

D.3 inches

Explanation: Per IPC Table 916.1, the minimum vent size for a water closet (3-inch drain) is 1-1/2 inches. Vent sizing depends on the drain size, the number of fixture units, and the developed length of the vent pipe. Proper venting protects trap seals.

10What is the minimum air gap for a lavatory indirect waste connection per the IPC?

A.1/2 inch

B.1 inch

C.Twice the effective opening diameter

D.Three times the pipe diameter

Explanation: Per IPC Section 608.15.1, an air gap must be at least twice the effective diameter of the opening through which water is supplied. For indirect waste connections, the air gap prevents contaminated water from being siphoned back into the potable supply.

About the DC Plumber Exam

The DC journeyman plumber exam is administered by PSI under the DCRA. It tests IPC knowledge including drainage systems, water supply, venting, gas piping, fixtures, and DC-specific code amendments for urban plumbing installations.

Questions

80 scored questions

Time Limit

3 hours

Passing Score

70%

Exam Fee

~$305 (DC Department of Consumer and Regulatory Affairs (DCRA))

DC Plumber Exam Content Outline

25%

Drainage & Waste Systems

Drain sizing, fixture units, slope requirements, cleanouts, and building sewer connections per IPC

20%

Water Supply & Distribution

Pipe sizing, backflow prevention, water heaters, pressure regulation, and cross-connection control

20%

Venting Systems

Vent sizing, wet venting, air admittance valves, vent termination, and circuit venting per IPC

15%

Gas Piping

Gas pipe sizing, appliance venting, pressure testing, BTU calculations per IFGC

20%

Fixtures, Materials & Code Administration

Fixture installation, materials, joints, permits, inspections, and DC-specific requirements

How to Pass the DC Plumber Exam

What You Need to Know

Passing score: 70%
Exam length: 80 questions
Time limit: 3 hours
Exam fee: ~$305

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

DC Plumber Study Tips from Top Performers

1Master IPC drainage fixture unit (DFU) values and pipe sizing tables

2Study backflow prevention device selection for DC's urban water systems

3Memorize minimum pipe sizes, slopes, and clearances for common fixtures

4Practice gas pipe sizing calculations using IFGC tables

5Understand wet venting and circuit venting provisions in the IPC

6Learn DC-specific permit and inspection requirements under DCRA

Frequently Asked Questions

What code does DC use for the plumber exam?

DC uses the International Plumbing Code (IPC) with DC-specific amendments enforced by DCRA. The exam covers IPC provisions for drainage, venting, water supply, gas piping, and fixture requirements.

Who administers the DC plumber exam?

The exam is administered by PSI on behalf of the DC Department of Consumer and Regulatory Affairs (DCRA). Candidates must apply through DCRA and schedule with PSI after approval.

How many questions are on the DC plumber exam?

The DC plumber exam has approximately 80 multiple-choice questions with a 3-hour time limit. A score of 70% or higher is required to pass.

Is the DC plumber exam open book?

Yes, PSI-administered plumber exams typically allow a bound copy of the adopted IPC. No loose papers, handwritten notes, or electronic devices are permitted. Check with DCRA for approved reference materials.