Master Plumber DWV and Storm Drainage Questions and Answers

Question 1

According to most plumbing codes, what is the minimum required air pressure and duration for testing a DWV (Drain, Waste, and Vent) system?

Accepted Answer

5 psi for 15 minutes

Answer

Standard plumbing codes, such as the IPC and UPC, typically require a DWV system to be tested with air at 5 psi for a duration of 15 minutes without any drop in pressure. This test ensures the system is airtight and free of leaks.

Question 2

A plumber is installing a horizontal drainage line for a series of sinks in a commercial building. The total developed length of the 4-inch pipe run is 120 feet. According to common plumbing codes, how many cleanouts are required for this section of piping?

Accepted Answer

One at the beginning, one at the end, and one in the middle

Answer

Most plumbing codes require a cleanout at the upper terminal of a horizontal drain and an additional cleanout for each 100 feet of developed length, or fraction thereof. Since the run is 120 feet, it requires a cleanout at the beginning, one for the first 100 feet, and another for the remaining 20 feet, which is often placed at the end of the run. Therefore, three cleanouts are necessary.

Question 3

Which of the following is an unacceptable practice when designing or installing a storm drainage system?

Accepted Answer

Connecting the primary roof drain system directly to the sanitary sewer system.

Answer

It is a fundamental plumbing principle and a strict code requirement that storm water drainage systems must be kept separate from sanitary sewer systems. Combining them can overwhelm sewage treatment facilities during heavy rainfall, leading to untreated sewage discharges.

Question 4

In a DWV system, what is the primary purpose of a vent?

Accepted Answer

To equalize air pressure within the drainage system, protecting fixture trap seals from siphonage and back pressure.

Answer

The vent system is crucial for maintaining neutral air pressure in the drainage pipes. As water flows down a drain, it can create negative pressure (siphonage) that pulls water from fixture traps, or positive pressure (back pressure) that pushes sewer gas through the trap. Vents allow air to enter and exit the system, preventing these issues and ensuring smooth drainage.

Question 5

A master plumber is overseeing the installation of an under-floor cleanout in a crawl space with limited access. According to the Uniform Plumbing Code (UPC), what is the maximum distance the cleanout can be from an access door or crawl hole?

Accepted Answer

5 feet

Answer

The Uniform Plumbing Code (UPC) specifies that an under-floor cleanout shall not be located more than 5 feet from an access door, trap door, or crawl hole to ensure it is readily accessible for maintenance and rodding.

Master Plumber Exam Practice Test

Master Plumber Exam Practice Test

Master Plumber DWV and Storm Drainage Questions and Answers