Considering all the things that you put down your kitchen sink, it's a wonder that they don't emit a bad smell all of the time. The reason they don't is because of an invention called a trap. These are located just underneath the drain and commonly form a U or J-shape. It was invented by Thomas Crapper in 1880 as an improvement over the original S-trap. If your sink is starting to emit a bad smell, then there's something wrong with your trap.
What Does The Trap Do?
Just as the name suggests, the trap traps small amounts of water in the bottom of the U-shape. This water forms a seal that gases can't get past. So even though your sink empties into the main drainage line of your home (where everything gets drained from toilets to showers to washing machines), you don't get any sewer gases leaking back up to wrinkle your nose.
Why Does It Stink?
So if your sink is starting to smell, the most likely reason is that the water has evaporated from the trap. This happens when you haven't been home for a while or haven't run water. It could also be because there is a leak in the trap. The easiest way to check for a leak in your trap takes two steps. First, dry the pipe underneath your sink completely with a towel. Then have someone turn on the cold water. Use your finger to feel around the joints and at the bottom of the U. If you feel water, you have a leak.
How to Fix It?
The easiest way to stop the smell is to replace the water in the trap. Use hot (not boiling) water and a little dish soap and rinse your drain. Then, pour three cups of cool water into the drain to make a new water seal.
If you have a leaky trap, it only takes a couple of hours to fix. Most traps have two screw connections, one on each end. Place a bucket underneath the old trap and use a pipe wrench to unscrew it. The bucket will catch whatever water and debris are still in the trap. Go to your local hardware store and get an identical trap and gasket set. Take it home and reinstall it according to the directions on the package. Make sure not to overtighten the screws or you could crack the pipe.
If you have a non-traditional setup in your sink or you aren't comfortable doing your own repairs, you should definitely get in touch with a licensed professional, like one from Midwestern Plumbing Service. When it comes to your plumbing, it's always better to be safe than sorry.