There is a constant bad smell coming from my kitchen sink, but the water drains fine and nothing is leaking. I have a dishwasher but no garbage disposal. What is causing it and how do I get rid of it?
When a kitchen sink drains well but smells all the time, the cause is almost always gunk, not a blockage. Grease, food scraps and soap build a slimy film inside the drain, the curved trap under the sink, and the spot where the dishwasher hose joins the drain. Bacteria in that film give off the smell. Start with a cleaning flush. Pour about a cup of baking soda into the drain, then slowly add a cup of white vinegar and let it fizz for about 10 minutes. Then flush it with hot water. Most kitchen drains under the sink are plastic (PVC or ABS), so let a boiled kettle cool for a minute or two first. Hot tap water or slightly cooled kettle water is fine, but a full rolling boil can soften plastic joints over time. While you wait, scrub the sink strainer basket and the underside of the drain opening with an old toothbrush, because a lot of the smell lives there. Next, check the dishwasher. Clean its filter, which usually twists out of the floor of the tub, and look under the sink at the dishwasher drain hose. It should rise in a high loop up to the underside of the counter, or run to an air gap, before it joins the sink drain. If it sags low, dirty sink water can drain back into the hose and sit there. If the smell comes back within a few days, put a bucket under the trap, unscrew the two slip nuts by hand, and rinse the trap out. If the smell is like rotten eggs or sewage rather than old food, the trap may be losing its water seal or the drain vent may be blocked. That needs a plumber to look at.
The baking soda and vinegar worked, but how do I stop the smell coming back?
Once a week, run hot tap water down the drain for a minute after washing greasy dishes, and never pour cooking fat or oil down the sink. Once a month, repeat the baking soda and vinegar flush, scrub the strainer basket, and clean the dishwasher filter. If the smell keeps returning even with that routine, remove and clean the trap, and check that the dishwasher hose has a high loop.
