Help, My Sink Drain Smells Like A Sewer!

With the holidays just around the corner, you're likely to have company dropping by, perhaps even a few surprise guests. You know, the guests that you must impress! The last thing you want is for your relatives and friends to be overcome with offensive odors emanating from your sink or shower drain? Keeping your drain pipes flowing freely is one of those reoccurring maintenance tasks accomplished with little effort.

First, inspect the sink bowl or floor drain area for any buildup of sludge on the stopper, drain cover, or top of drain pipe. On sinks, as you pull the stopper out, you'll know pretty quickly if this is your issue...let's just say, gross! When you have this issue, the foul odor may also seem to disappear at times, but rear it's ugly head as you run warm water. This can be remedied by just flushing with a tea kettle of boiling water every month or so.

Next, have you considered a buildup of hair and sludge at the sink stopper level just inside the drain?  Usually a small, stiff wire at least 10 inches long and bent into a ‘U” at one end will allow you to fish out any obstructions. Be mindful not to throw this back into the drain system, but rather place with trash. Again, flush the drain with boiling water.

Lastly, consider the configuration of your DWV (drain, waste, ventilation) system. In many instances this is most easily accomplished by looking under the bathroom, kitchen, or utility sink. It will be more difficult to determine this with showers and tubs as their drain configurations are most likely contained within finished walls. You may have to do a little more exploring. What you expect to see when viewing a household drain near the point of entry is the presence of a trap. The trap keeps sewer gas at bay by "trapping" water in the U-shaped portion of the pipe, forming a water seal. The water blocks the movement of upward sewer gas and prevents it from migrating through the trap, the sink and into the room.

The sewer-like odor or gurgling sound is most commonly experienced with non-vented S-traps (right), as opposed to vented P-traps. S-traps, even though they are no longer permitted to be used in new construction, are prevalent in older homes. The problem with an S-trap is that the water seal may be lost due to siphonage. The action of the water discharging into the drainpipe removes the air from that pipe and thereby causes a negative pressure, or vacuum, in the drain line, resulting in siphonage of the water from the trap. Once the water seal is lost, sewer gas can flow freely into the room.

Siphonage is unlikely when a vented P-trap (right) is used. The horizontal portion of the trap is connected to a plumbing vent pipe, which extends through the roof, so there is always atmospheric pressure on the downward side of the drain.

Should you find, as in many older homes, you do have an “S” trap configuration and have frequently noticed sewer gas smells, I suggest the services of a professional plumber to install the correct and acceptable configuration.
As a side note, should you decide to clean your drain with chemicals before calling the plumber, be very careful to choose a non toxic and environmentally safe drain cleaner. A little research to find the right product will go a long ways in protecting you, your home, and the environment. For simple clogs and sludge build-up, strong chemicals aren't really needed anyway--hot water and stiff wire are cheap and work best.