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Under Oklahoma's adoption of the IPC, what is the minimum size drain pipe permitted for a water closet?

2 inches

3 inches

4 inches

1-1/2 inches

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Key Facts: OK Plumber Exam

70%

Passing Score

Construction Industries Board

Questions

3 hours

$75-330

Exam Fee

PSI

IPC

Code

Construction Industries Board

Oklahoma's journeyman plumber exam is administered by PSI on behalf of the Construction Industries Board. It has approximately 80 questions with a 3 hours time limit and requires 70% to pass. The exam fee is $75-330. Oklahoma uses the IPC as its plumbing code.

Sample OK Plumber Practice Questions

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

1Under Oklahoma's adoption of the IPC, what is the minimum size drain pipe permitted for a water closet?

A.2 inches

B.3 inches

C.4 inches

D.1-1/2 inches

Explanation: Per the IPC as adopted by Oklahoma, the minimum drain pipe size for a water closet is 3 inches. This is a fundamental sizing requirement that ensures adequate flow capacity for the fixture discharge. A 4-inch pipe is required for building drains and sewers receiving discharge from water closets in many situations, but the individual fixture drain minimum is 3 inches.

2According to Oklahoma plumbing regulations enforced by the Construction Industries Board, what is the minimum slope required for a 4-inch horizontal drainage pipe?

A.1/4 inch per foot

B.1/8 inch per foot

C.1/2 inch per foot

D.1/16 inch per foot

Explanation: Per the IPC, 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. The reduced slope for larger pipes is permitted because the greater cross-sectional area provides adequate self-scouring velocity at the lower gradient.

3What is the maximum distance a P-trap can be located from the vent fitting it serves under Oklahoma's IPC adoption?

A.The developed length cannot exceed the values in Table 906.1 based on trap size

B.6 feet from any trap regardless of size

C.10 feet from the trap

D.There is no maximum distance

Explanation: The IPC Table 906.1 establishes the maximum developed length between a trap and its vent based on the trap arm size. For example, a 1-1/2 inch trap arm has a maximum distance of 6 feet, while a 2-inch trap arm can extend up to 8 feet. These distances ensure the vent can protect the trap seal from siphonage.

4In Oklahoma, what type of backflow preventer is required to protect the potable water supply from a high-hazard cross-connection?

A.Reduced pressure zone (RPZ) backflow preventer

B.Atmospheric vacuum breaker (AVB)

C.Dual check valve

D.Hose bibb vacuum breaker

Explanation: A reduced pressure zone (RPZ) backflow preventer is required for high-hazard cross-connections where a health hazard exists. The RPZ contains two independently operating check valves with a differential pressure relief valve between them that opens to atmosphere if either check valve fails. This provides the highest level of protection for potable water supplies.

5Under the IPC as enforced in Oklahoma, what is the DFU (Drainage Fixture Unit) value assigned to a residential water closet with a 1.6 GPF flush?

A.2 DFU

B.3 DFU

C.4 DFU

D.6 DFU

Explanation: Per IPC Table 709.1, a water closet with a flush volume of 1.6 gallons per flush or less is rated at 3 DFU. This value is used for sizing drainage piping systems. Older water closets rated above 1.6 GPF are assigned 4 DFU, reflecting their greater discharge volume.

6According to Oklahoma regulations, what is the minimum air gap required for an indirect waste receptor serving a commercial dishwasher?

A.1 inch or twice the diameter of the drain, whichever is greater

B.1/2 inch

C.2 inches

D.Equal to the pipe diameter

Explanation: Per the IPC, the minimum air gap for indirect waste connections is 1 inch or twice the effective opening of the drain pipe, whichever is greater. This air gap prevents contamination from the receptor from reaching the indirect waste pipe through backflow or backsiphonage.

7What is the maximum working pressure allowed for a gas piping system test in Oklahoma per the IPC/IFGC?

A.Test at not less than 3 psig for 10 minutes

B.Test at not less than 10 psig for 15 minutes

C.Test at not less than 1/2 psig for 30 minutes

D.Test at not less than 5 psig for 5 minutes

Explanation: Per the IFGC Section 406.4, gas piping systems operating at 14 inches water column or less shall be tested at not less than 3 psig (approximately 6.9 kPa) for a minimum of 10 minutes. The test duration and pressure ensure that even small leaks will be detected. The system must show no drop in pressure during the test period.

8Under Oklahoma's IPC adoption, what is the minimum vent pipe size that can be used?

A.1 inch

B.1-1/4 inches

C.1-1/2 inches

D.2 inches

Explanation: Per the IPC, the minimum vent pipe size is 1-1/4 inches. However, the vent size must also be not less than one-half the required size of the drain served. Individual vents for water closets must be a minimum of 1-1/2 inches or 2 inches depending on the developed length.

9In Oklahoma, when is a cleanout required on a horizontal drainage pipe?

A.At each change of direction greater than 45 degrees

B.At each change of direction greater than 90 degrees

C.Only at the building drain connection

D.Every 25 feet regardless of direction changes

Explanation: Per the IPC, cleanouts are required at each change of direction exceeding 45 degrees in horizontal drainage piping. This allows access for clearing blockages at points where solids are most likely to accumulate. Additional cleanouts are required at intervals not exceeding 100 feet for 4-inch and larger pipes.

10According to the IPC as adopted in Oklahoma, what is the maximum temperature setting for a residential water heater thermostat?

A.120°F

B.140°F

C.130°F

D.160°F

Explanation: The IPC limits residential water heater thermostats to a maximum setting of 140°F. While 120°F is often recommended to prevent scalding, the code maximum is 140°F. Anti-scald devices or thermostatic mixing valves are required at certain fixtures to limit delivery temperature to 120°F at showers and bathtubs.

About the OK Plumber Exam

Oklahoma-specific journeyman plumber licensing exam based on the IPC covering drainage, water supply, venting, gas piping, and fixtures

Questions

80 scored questions

Time Limit

3 hours

Passing Score

70%

Exam Fee

$75-330 (Construction Industries Board / PSI)

OK Plumber Exam Content Outline

25%

Drainage Systems & Pipe Sizing

Drain sizing, fixture units (DFU), slope requirements, cleanouts, building drain and sewer sizing per IPC

20%

Water Supply & Distribution

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

20%

Venting Systems

Vent sizing, wet venting, air admittance valves, vent termination, circuit venting, and combination waste and vent

15%

Fixtures & Appliances

Fixture installation, clearances, water heaters, accessible fixtures, and commercial fixture requirements

10%

Gas Piping

Gas pipe sizing, appliance venting, pressure testing, BTU calculations, CSST bonding, and combustion air

10%

Code Administration & Special Systems

Permits, inspections, plan review, Oklahoma state amendments, medical gas, grease interceptors, and storm drainage

How to Pass the OK Plumber Exam

What You Need to Know

Passing score: 70%
Exam length: 80 questions
Time limit: 3 hours
Exam fee: $75-330

Keys to Passing

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

OK Plumber Study Tips from Top Performers

1Master DFU values and drain pipe sizing — heavily tested on every exam

2Memorize minimum pipe sizes, slopes, and fixture clearances from code tables

3Practice backflow prevention device selection for different hazard levels

4Study gas piping sizing, pressure testing, and combustion air requirements

5Learn to navigate the IPC index quickly for efficient code lookup

6Review water heater installation including T&P valve requirements

7Practice with timed exams to develop time management skills

8Focus on venting methods — wet venting, circuit venting, and AAV rules

Frequently Asked Questions

What plumbing code does Oklahoma use?

Oklahoma uses the IPC for its plumbing licensing exam. Candidates should study the current adopted edition with any state-specific amendments.

Who administers the Oklahoma plumber exam?

The exam is administered by PSI on behalf of the Construction Industries Board. Register through PSI after your application is approved.

What is the passing score?

Oklahoma requires 70% to pass the journeyman plumber exam. The exam has 80 questions with a 3 hours time limit.

Is the exam open book?

Most PSI-administered plumbing exams allow a bound copy of the adopted plumbing code. No loose pages, handwritten notes, or electronic devices are permitted. Check current exam policies before your test date.