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Smelly Drains: Diagnosing and Fixing Them – Boston, Worcester

16 Apr 2014

Drains can really start to smell, and some of those odors can be pretty bad, including the smell of sewage. Here is what to do -- and what not to do – about it.

Considering what they do, it’s a miracle that drains don’t smell up our homes all the time. What happens when your drain is suddenly smelly? Most likely, it’s one of two things: crud inside the pipe (which may be related to a clog) and sewer gas (which is always present in part of your drain system but isn’t supposed to get into the house). Usually a smelly drain problem is easy to solve.

Which One Stinks

Sometimes it’s hard to know which drain smells, so here’s a simple trick: Cover the suspected smelly drain opening with tape or a plastic bag (or both). Let the room air out for a bit. If the smell is gone, you’ve found the culprit. If not, move the tape or bag to the next likely suspect and test again.

Clogs and Crud

A really dirty drain can smell enough to carry into a room, and there are a couple of good clues that this is the source of your problem. A slow drain is one indication. A partially clogged drain doesn’t get rid of waste effectively, leading to more crud buildup. Ultimately, this may lead to a total clog, but it can take a long time. Meanwhile, the buildup just gets worse. The solution is to clean the drain thoroughly with a snake If you don’t know how or if you don’t know what this means, call a plumber.

The other way to tell if your problem is crud is the smell. A dirty drain smells bad, but there’s nothing like the gaseous pungency of sewage. Sewage smell indicates a different drain problem.

A few drains that are most prone to crud-related smells and their solutions:

  • Bathroom sink: The drain stopper assembly catches hair — then everything else — several inches below the drain opening. Remove the stopper and clean this section of pipe periodically to eliminate odors.
  • Tub/shower drain: Hair clogs lead to soap buildup and badly gunked pipes; clean thoroughly with a snake.
  • Kitchen sink: Garbage disposers are the culprits more often than drains. Freshen inside the disposer with Borax or a commercial disposer cleaner, and clean the gunk from the underside of the rubber baffle around the drain opening (you have to do this by hand, and it’s not pretty, but it works).

Smells like Sewage

If your drain smells like sewage, most likely it is sewage or sewer gas. Every drain in your house has a trap — a U-shaped piece of pipe that holds a small amount of water at all times. The water serves as a plug to keep sewer gas from rising up the drain. This works beautifully unless one of the following happens:

  • The original plumber or remodeler failed to install a trap, in which case you’d probably smell gas all the time.
  • The drain isn’t properly vented, and a suction effect in the system siphons the trap dry. The same thing can happen if the vent is blocked (from tree leaves, bird nests, snow, etc.).
  • The fixture served by the drain is too close to other fixtures, such as a toilet drain that’s too close to a sink drain; the force of the toilet flush can siphon the sink trap dry.

If you suspect a dry trap, run water in the fixture slowly for a few minutes, then shut it off This should fill the trap and stop the sewer smell. This can help diagnose the problem but not solve it. However, most venting problems can be remedied by installing an Air Admittance Valve (AAV), a pipe-less air vent that can go almost anywhere along a drain line. A plumber can help with this.

For more help, contact Greater Boston Plumbing and Heating.