There’s a foul odor emanating from under our bathroom sink. It started a couple of months ago and the smell comes and goes. Help! – Janelle

Hi Janelle,

There are several possible reasons why an odor could be coming from under your bathroom sink, including problems with the drain trap, vent pipe, or under your house. Here’s how to go about checking each of them.

Sink Trap and Drain

I’d start by checking the trap and drain under the sink. The curve in the trap holds water to prevent sewer gas from seeping back into the living space from the drain pipe. If the water leaks out of the trap, it can break the seal and allow unpleasant orders into the house.

Check to be sure the trap and other drain pipe components are tight, not leaking, and that the trap is full of water. You also might want to pour disinfectant or bathroom cleaner down the drain to kill any mold or other causes of odors.

Sink Drain Vent Pipe

Next, I would check the vent pipe – that’s the pipe that goes from the drain up through the roof to allow outside air in when a fixture is draining. If the vent pipe is clogged, obstructed, or wasn’t installed properly, it can draw the water out of traps in nearby fixtures.

Run a plumbing snake as far down the vent pipe as you can to clear it.

Dead Animals

If you still have an odor problem, check the crawlspace under your house, behind the bathroom wall, or under the vanity to see if you might have a dead animal.

A digital inspection camera – such as the Ridgid SeeSnake, Milwaukee M-Spector Cordless Camera, or Ryobi TEK4 Inspection Scope, works great for checking the drain, vent pipe, inside walls, or under the house.

Good luck with your project,

Further Information

• How to Position a Vent Pipe (article)
• How to Clean Out a Tub Drain (video)

Tags: , bathroom, odor, Plumbing