Home Inspector Plumbing DWV Systems Questions and Answers

Question 1

During a home inspection, you observe a kitchen sink drain that makes a 'gurgling' sound after water has been drained and a faint sewer gas odor is present. What is the MOST likely cause of these issues?

Accepted Answer

A blocked or improperly installed vent stack.

Answer

The vent stack's primary functions are to allow sewer gases to escape to the exterior and to introduce air into the DWV system to prevent a vacuum. Gurgling sounds and sewer odors are classic signs that the vent is blocked or improperly installed, causing negative pressure that siphons water from the P-trap, breaking the water seal that normally blocks sewer gas.

Question 2

What is the generally accepted minimum slope for a horizontal 3-inch drainpipe in a residential DWV system according to most plumbing codes?

Accepted Answer

1/8 inch per foot

Answer

According to the International Plumbing Code, the minimum slope for a horizontal drainage pipe with a diameter of 3 to 6 inches is 1/8 inch per foot. This slope is crucial for ensuring that solid waste is carried along with liquids, preventing clogs. A slope of 1/4 inch per foot is required for pipes 2 1/2 inches or smaller.

Question 3

A home inspector identifies a sink drain with an 'S-trap' configuration. Which of the following statements BEST describes the issue with this type of trap?

Accepted Answer

It is susceptible to self-siphoning, which can remove the water seal.

Answer

S-traps are prohibited by modern plumbing codes because their design, which drains straight down, can create a siphon effect that pulls the water out of the trap. This removes the water seal that is necessary to block sewer gases from entering the home. P-traps, which connect to a horizontal drain line in the wall, are designed to work with a vent system to prevent this siphoning.

Question 4

What is the primary purpose of a P-trap in a plumbing drain waste and vent (DWV) system?

Accepted Answer

To hold a small amount of water to block sewer gases.

Answer

A P-trap is a U-shaped pipe designed to constantly hold a small amount of water. This water acts as a seal, effectively blocking unpleasant and potentially harmful sewer gases from backing up through the drain and into the living space.

Question 5

While inspecting a newly installed bathroom sink, you notice the trap arm, which is a 1 1/2-inch pipe, connects to the vent stack only 2 inches from the trap weir. This installation is a defect because:

Accepted Answer

The vent connection is too close, creating a prohibited crown vent.

Answer

Plumbing codes require a minimum distance between the trap weir and the vent to prevent siphoning. This minimum distance is two times the pipe's diameter. For a 1 1/2-inch pipe, the minimum trap arm length is 3 inches (1.5 x 2). An installation with only 2 inches creates a 'crown vent,' which is prohibited because it can easily become clogged and lead to the trap siphoning dry.

Home Inspector Test Practice Test

Home Inspector Test Practice Test

Home Inspector Plumbing DWV Systems Questions and Answers