An odor of rotten eggs or sewage in a basin or sink is usually caused by sewer gases forming in the household drain. These gases are formed by bacteria that live on food, soap, hair, and other organic matter in the drain. These gases are heavier than air and remain in the drain until the water is turned on. As the water runs down the drain, the gases are expelled into the atmosphere around the sink. It is natural to associate these odors with the water because they are observed only when the water is turned on. However, the odor is not in the water - it is simply the water pushing the gas out of the drain. To eliminate this problem, the bacteria in the drain must be killed. This process is called disinfecting the drain and is outlined in the following six steps. Caution: Do not mix any drain cleaners or detergents with bleach. Certain combinations can create toxic fumes.

1. Run the cold water for about 15 seconds into the drain that is to be disinfected, then turn the water off.
2. Pour approximately one to two cups of liquid chlorine bleach (laundry bleach) down the drain(s) where the odor is present. Pour the bleach slowly around the edges of the drain so that it runs down the sides of the drain. Caution: Bleach may cause eye damage, skin irritation, and may damage clothing - BE CAREFUL!
3. If the odor is coming from a sink with a garbage disposal, turn the disposal on for a few seconds while the bleach is being poured. This will disperse the bleach around the inside of the disposal. Caution: Bleach may cause eye damage, skin irritation, and may damage clothing. Take care to avoid splashing for the few seconds the disposal is turned on.
4. Allow the bleach to remain undisturbed in the drain for about 10 minutes.
5. After 10 minutes, run hot water into the drain for a minute or two to thoroughly flush out the bleach. If a garbage disposal was disinfected, thoroughly flush it as well. Caution: Prolonged contact with metals may cause pitting and/or discoloration.
6. This procedure may need to be repeated if the odor returns.