Bad smells coming from a sink or shower drain are not uncommon. Drains are breeding grounds for bacteria that can emit a foul odour. Kitchen sinks in particular often are the worst offenders with all the bits of food that end up clinging to the sides of the drain. Keep your drain odour-free by giving it good deep-cleaning every few weeks.
The two primary causes of foul odours in sink drains are bacteria and rotten food or gunk, which may consist of trapped hair, soap and dirt. Bacteria often accumulate in areas where the pipe bends or in pipes that aren't used often, such as the pipe that serves the overflow area in a bathroom sink. The smell it gives off is similar to rotten eggs and is quite unpleasant. Rotting food and gunk emit an equally unpleasant odour, but it is more organic. Other, less common causes are a sewer backup or too many sulphates in the water, which can happen if you have a well. Have the water tested immediately if you suspect the odour arises from one of these problems, as the solutions to both will require calling a professional.
Liquid bleach kills bacteria on contact and will eliminate the accompanying odour. Wear some gloves to protect your hands and open nearby windows, as bleach has a strong odour. Then, simply pour the bleach down the drain, whether it's a shower, kitchen or overflow drain. You may have to repeat this when you smell the odour again, as it is not a permanent solution.
Accumulated gunk must be cleaned away to get rid of the odour. Mix up a solution that will eat away at the slime and freshen your drain at the same time. Place 1 cup of vinegar in a saucepan on medium heat on the stove. Pour 1/4 cup salt into a bowl, and add 1/2 cup baking soda. Stir the dry ingredients together, and then pour the mixture down the drain. Follow it up immediately with the warm vinegar. When the vinegar hits the baking soda, the ensuing reaction will form bubbles that will eat away at slime and gunk trapped in your sink. Leave it alone for 15 minutes, and then rinse with hot water straight from the tap.
Tips and Tricks
Keep bits of food particles, hair and dirt to a minimum by installing a fine-mesh cover over your drain. This will catch the debris before it can rot in the drain. Empty the cover periodically or else the gunk will simply rot in the cover instead of the drain.