To get rid of a smelly kitchen sink, find the source. Most smells are food and grease in the disposal, under its rubber baffle, or in the trap. Scrub the baffle, flush with hot water, and put grease in the trash. A sewer smell points to a dry trap, a bad vent, or a sagging dishwasher hose.
How do you tell food odor from sewer gas?
By the smell and by when it shows up:
| What you notice | Likely cause | Where to look |
|---|---|---|
| Sour or rotten food, worse near the drain opening | Food buildup | Disposal, splash guard, drain basket |
| Smell right after running the disposal | Food trapped in the grind chamber or under the baffle | Disposal |
| Musty smell after running the dishwasher | Dirty water sitting in the hose or at the sink connection | Dishwasher drain hose |
| Rotten eggs, strongest after the sink sits unused | Dry trap | Trap under the sink |
| Rotten eggs plus gurgling when other fixtures drain | Venting problem | Vent pipe or air admittance valve |
| Sewage smell in several drains at once | Main line or vent problem | Call a plumber |
The rotten-egg smell is hydrogen sulfide, the main part of sewer gas. ATSDR, part of the CDC, says it "is a flammable, colorless gas that smells like rotten eggs," that people "usually can smell hydrogen sulfide at low concentrations," and that "It is often referred to as sewer gas or stink damp." A faint whiff at a sink is a nuisance. A strong, lasting sewer smell in the house needs a plumber.
How do you get rid of a food smell?
Clean where food collects, starting with the disposal. InSinkErator, a major disposal maker, says "if you smell any odors coming from your disposal, it's usually the sign of food build up," and "Over time, food waste can also accumulate under the sink baffle." The baffle is the rubber splash guard in the sink opening.
Its cleaning steps, in order:
- 1Turn off the disposal. Unplug it or switch off the wall switch before you put a hand near the opening.
- 2Remove the baffle and clean it. InSinkErator says to "clean the underside of the baffle with a scouring pad." The underside is usually where the black gunk and smell live.
- 3Put the baffle back and run cold water with the disposal on.
- 4Freshen it. The maker suggests "ice cubes mixed with lemon/lime wedges down your disposal to freshen it up."
Then deal with the drain itself:
- Clean the drain basket on the second bowl, if you have one.
- Flush the line. Run hot water for a minute or two after each use of the disposal so scraps clear the trap.
- Keep grease out. The City of Phoenix says "Grease is the most frequent cause of sewer problems," and that cooking grease poured down a drain, "even when followed by hot water, it eventually cools down, congeals, builds up, and hardens." The city's fix: "allow the grease or cooking oil to cool, then dispose of it with the garbage."
Our page on why a garbage disposal smells bad goes deeper on the disposal, and black slime in drains explains the biofilm that builds up in sink drains.
### Is it safe to use bleach or drain cleaner?
Be careful. The CDC says to never "mix bleach with ammonia or any other cleaner." A CDC report adds that "Mixing of bleach solutions with vinegar or ammonia, as well as application of heat, can generate chlorine and chloramine gases that might result in severe lung tissue damage when inhaled." Don't follow a chemical drain cleaner with another product, and don't use a plunger on a sink that's full of drain cleaner. For a slow or smelly drain, a plunger or a drain snake is safer than chemicals, and hot water and a scrub brush handle most food odors.
What if it smells like sewer gas?
Then the problem is the barrier that keeps sewer gas in the pipes. Every sink has a trap, the U-shaped bend under it, which holds water to block the gas. The plumbing code puts it simply: "The trap seal of a trap is an essential feature of a drainage system to prevent odors from the drainage piping from entering the building." Section 1002.4 requires a seal "of not less than 2 inches (51 mm) and not more than 4 inches (102 mm)."
Three things break that seal:
1. The trap dried out. A sink that goes unused for weeks, in a vacation home or a spare prep sink, loses its water to evaporation. Phoenix heat speeds that up. Run water for a minute to refill it. See what a P-trap is.
2. The vent isn't working. The drain needs air to flow smoothly. The code says the vent system must keep any trap seal from seeing "a pressure differential of more than 1 inch of water column." When the vent is blocked, draining water can pull the trap seal out behind it, and you'll often hear gurgling. Many kitchen islands use an air admittance valve instead of a vent through the roof. These must "conform to ASSE 1051," and they can wear out and stick. See what an air admittance valve is and why a kitchen sink gurgles when the dishwasher drains.
3. The trap or drain connection is leaking. A loose slip nut or a cracked trap lets gas and water escape under the sink. Look for moisture or a smell stronger inside the cabinet than at the sink.
Can the dishwasher make the sink smell?
Yes, when its drain hose is installed wrong. A dishwasher drains into the sink drain, and if its hose is installed wrong, dirty water can sit in the hose or flow back from the sink. The code, in Section 409.4, says the dishwasher waste "shall connect directly to a wye branch fitting on the tailpiece of the kitchen sink, directly to the dishwasher connection of a food waste disposer, or through an air break to a standpipe," and that "The waste line of a residential dishwasher shall rise and be securely fastened to the underside of the sink rim or countertop."
That rise is called a high loop. Bosch's installation guide says "The dishwasher drain hose must be installed with a portion of it at least 20” (508mm) off the cabinet floor; otherwise the dishwasher may not drain properly." Check under the sink: if the hose sags along the cabinet floor with no high point, clip it up under the counter. Some homes use an air gap fitting on the countertop instead. See what a dishwasher air gap is.
If the dishwasher is also leaving water in the bottom, the drain problem is bigger than a smell. See why a dishwasher won't drain.
When should you call a plumber?
When the easy fixes don't work, or the smell points past the sink:
- The sewer smell comes back within a day of refilling the trap.
- More than one drain smells, or drains are slow all over the house.
- The sink gurgles every time another fixture drains.
- You see water or feel dampness under the cabinet.
- The smell is strong enough to notice through the house.
A plumber can check the trap and connections, test the vent or replace a failed air admittance valve, clear buildup from the line with a snake or jetter, and, for a smell that won't give up its source, run a smoke test to find where sewer gas gets in. For a sewer smell that's more than a single sink, see why a bathroom drain smells like sewer, which covers the same causes elsewhere in the house.
HQ Plumbing & Air fixes smelly and slow kitchen drains, replaces traps and air admittance valves, corrects dishwasher drain connections, and runs smoke tests to track down sewer gas across the Phoenix area. We're licensed and insured, with free estimates and upfront pricing. See our drain cleaning service.
Clean the baffle, keep the grease out, and keep water in the trap. That handles most smelly sinks.