Foul smells emanating from your sink or garbage disposal generally indicate that a piece of food or other organic matter is caught in the pipes. As the food decomposes, it releases a foul odor that is drawn up into your kitchen through the drain. Foul smells can also be caused by a bacterial imbalance in your pipes. Pour a solution of equal parts baking soda and vinegar down the drain. Wait five minutes, then pour boiling water down the drain. If this doesn’t eliminate the stench, call a plumber.