Rotten Food in Trap
Some kitchen sink drains have a trap in the drain that catches food. Food will collect in the U-shaped pipe.
The garbage disposal will eventually clean out these food particles, but if you don't run it in a while, the food particles will begin to rot and smell. This smell is reminiscent of rotten eggs, sulfur or a pungent chemical odor.
Contaminates in Drain
Soap scum, hair, dirt and other contaminates can cake on the inside of the drain, which will create a slimy, black substance that eventually can have a bad smell and can even clog your drain. Remove this by cleaning out the inside of your drains with a drain pipe cleaner every few months.
Fix bad smells in drains by running clear water through the drainpipes several times per month. If you have a garbage disposal, run the water down the drain and keep the garbage disposal running.
You can also put a few drops of liquid dish soap or some orange peels down the running garbage disposal to sweeten the smell. Alternatively, pour some baking soda down the drain, and let it sit for several minutes.
The baking soda will absorb the bad smell. Finish by running the disposal with water.
Prevent bad smells in your kitchen sink by not putting food down the drain unless you run your garbage disposal with water until you hear that the food has run through the disposal. Fix your disposal whenever you notice that it is not working properly, which will not break up the food particles enough to run through the sink.
Instead, they will not break down and will rot in the sink.