Master Plumber – National Portion Exam

Try 10 realistic code-based plumbing questions before you buy the full practice exam.

Answer each question, then click “Check my score” at the bottom of the page. You’ll see your total score plus the correct answers for every item.

How this free practice exam works

This 10-question mini-exam is designed to mirror the style and cognitive level of the Master Plumber – National Portion exam, with a focus on commonly adopted plumbing code principles.

Choose one answer for each multiple-choice question.
Click “Check my score” to see how you did.
Instant feedback shows which questions are correct or incorrect and reveals the right answers.

This practice content is for exam preparation only and is not endorsed or approved by any state licensing board, code authority, or exam provider. Always refer to the most current plumbing code and your jurisdiction’s amendments.

Master Plumber – National Portion Exam (10 Questions)

Question 1

On this exam, horizontal drainage piping that is 3 inches in diameter is typically required to be installed with a minimum slope to maintain proper flow. Based on commonly adopted plumbing codes, that minimum slope is:

A. 1/8 inch per foot B. 1/4 inch per foot C. 1/2 inch per foot D. 1 inch per foot

Question 2

For test purposes, the main function of a trap installed under a fixture such as a lavatory or sink is to:

A. Increase water pressure at the fixture B. Eliminate the need for vent piping C. Provide a water seal to prevent sewer gases from entering the occupied space D. Reduce the velocity of water in the water supply piping

Question 3

On this exam you will see questions about venting. The primary purpose of the vent system in a plumbing installation is to:

A. Equalize air pressure in the drainage system to protect trap seals B. Increase water velocity in the drainage piping C. Provide a pathway for storm water to reach the sanitary sewer D. Replace the need for cleanouts at changes in direction

Question 4

A potable water supply is connected to a boiler that could allow contaminated water to flow back into the domestic system if pressure changes occur. A typical method shown on this exam to protect against backflow in this situation is to install a:

A. Standard swing check valve only B. Gate valve on the cold water supply line C. Globe valve on the hot water outlet D. Reduced-pressure principle backflow preventer or other approved backflow assembly

Question 5

A building drain is defined on this test as that part of the lowest piping of a drainage system that:

A. Extends from the street sewer to the property line B. Receives the discharge from soil, waste, and other drainage pipes inside the building and extends to 3 feet outside the building wall C. Serves only storm water from roof drains D. Is installed above the highest fixture on the top floor

Question 6

When a horizontal branch drain ties into a vertical stack, the fitting most commonly shown on this exam as acceptable for that connection is a:

A. Long-radius 90° elbow B. Straight tee with square corners C. Sanitary tee or combination wye and 1/8 bend designed for drainage flow D. Coupling installed with a slight offset

Question 7

A floor-mounted water closet is being rough-in installed. According to common code requirements emphasized on this exam, the center of the closet flange is typically set:

A. 12 inches from the finished wall behind the fixture, unless otherwise specified B. 8 inches from the finished wall behind the fixture C. 18 inches from the finished wall behind the fixture D. Even with the face of the wall studs before drywall is installed

Question 8

A hose bibb located outdoors is often shown on this exam as needing protection against back-siphonage. One commonly accepted device for this purpose is a:

A. Standard gate valve B. Swing check valve installed horizontally C. Globe valve with integral strainer D. Vacuum breaker or hose bibb vacuum breaker listed for the purpose

Question 9

On this exam, a hydrostatic test of a drainage and vent system is illustrated as being performed by:

A. Filling the system with air at 50 psi and checking for pressure loss B. Filling the system with water up to a specified height and checking for leaks over a set time C. Running all fixtures at full flow for 10 minutes D. Using smoke only to check for openings in the vent system

Question 10

For interior water distribution, this exam commonly presents questions on acceptable piping materials. Which of the following is generally considered suitable for domestic hot and cold water piping when installed in accordance with the manufacturer’s instructions and applicable code?

A. Standard ABS plastic pipe B. Galvanized drain-waste-vent (DWV) fittings only C. Type L copper or listed PEX tubing D. Nonmetallic electrical conduit