Vanity Plumbing Pipe Distance From a Wall

Vanity Plumbing

• The plumbing under a vanity consists of a drain, P-trap and pipe leading to the vent pipe. The P-trap under the drain creates a water block to prevent sewer gases from the waste pipe from flowing back up into the vanity, bringing noxious fumes with them. The distance from the P-trap to the vent pipe depends on the diameter of the pipe. Keeping the pipe distance to the vent pipe below the maximum allowed will ensure that the vanity sink drains properly.

Vent Pipe

• The vent pipe for a vanity runs inside the wall directly behind the vanity. The upper half of the pipe extends up to the roof to provide an air inlet for the plumbing. Without this inlet, a vacuum would be created inside the pipe, preventing water from draining. The bottom half of the vent pipe leads to the sewer drain with the rest of the waste plumbing lines in your home.

P-trap

• The P-trap is directly under the sink. The drainpipe flows down, but then it makes a U-shaped curve at the bottom before making a 90-degree turn at the end of the trap to flow into the vent pipe. When measuring the distance from your vanity's plumbing to the vent pipe inside the wall, use the end of the P-trap as your reference.

Distance to Vent

• Codes dictate how far you can install the vanity's plumbing from the vent in the wall. According to "Advanced Home Plumbing: Hundreds of Step-by-Step Photos" by Creative Publishing International, the maximum distance from the end of the P-trap to the vent pipe is determined by the diameter of the vanity's drain. For a 1 1/4-inch drain, the pipe must be less than 2 1/2 feet long. If you have a 1 1/2-inch drain, place the vent no more than 3 1/2 feet away from the end of the P-trap. For 2-inch, 3-inch or 4-inch pipes, place the vent pipe no more than five, six or 10 feet away, respectively.