How to Clean a Smelly P-Trap Under the Kitchen Sink

The trap has a second job: it holds water that blocks sewer gas. The International Plumbing Code requires each fixture trap to hold a water seal of 2 to 4 inches (ICC IPC Chapter 10). So a trap that leaks, or one that was put back wrong, can also cause a sewer smell.

Graphic: summary of this guide, made by our team from the cited sources.

What actually builds up in the trap

Seattle Public Utilities lists the foods that cause kitchen drain clogs (Seattle Public Utilities):

• Bacon grease and meat drippings
• Butter, margarine and cooking oils
• Gravy, sauces, soups and fatty leftovers
• Dairy such as milk, cream and cheese
• Oils that harden when cool, such as olive oil and coconut oil

Some common habits make it worse. Seattle says hot water and soap do not dissolve grease; it cools and sticks farther down the pipe. A garbage disposal only breaks food into smaller pieces, and grease still clogs. Spoiled milk is a liquid but solidifies over time (Seattle Public Utilities). Food scraps from a disposal can also clog pipes (Seattle Public Utilities).

That mix of fat and food sits in the bend of the trap. InSinkErator describes kitchen sink odor as coming from bacteria that form on food waste (InSinkErator).

What you need

Item	Why
Bucket or dishpan	Catches the water and gunk in the trap
Rubber gloves	The contents are greasy and smell
Slip-joint pliers	Loosens stuck nuts; wrap the jaws in a rag on chrome
Bottle brush or old toothbrush	Scrubs the inside of the trap
Dish soap and hot water	Cuts grease
Flashlight	Lets you look into the wall pipe

Step-by-step

1. Clear the cabinet and put the bucket under the trap. Don't run water while the trap is off.
2. Loosen the two slip nuts. One is on top where the trap meets the sink tailpiece; the other is where the trap meets the pipe going into the wall. Turn them counterclockwise by hand, or with pliers if stuck.
3. Pull the trap down and empty it into the bucket. Note which way the washers face; the beveled side usually faces the joint.
4. Scrub the trap with hot water, dish soap and a brush, outside or in a utility sink. Don't wash it in a sink that drains through the trap you just removed.
5. Look into the wall pipe with a flashlight. If it's lined with grease, scrape out what you can reach or run a small hand auger in a few feet.
6. Reinstall the trap, washers in place, and hand-tighten the nuts.
7. Run water for a minute and check both joints for drips. Tighten a little more if needed.

If you have a garbage disposal

The disposal itself can smell. InSinkErator suggests cleaning the underside of the rubber baffle and the inside of the grind chamber's upper lip with a scouring pad, with the power off and your hand never inside the disposal, and then running the disposal with a mixture of 1/4 cup of baking soda and water (InSinkErator). It also says to run cold water while grinding and never put grease into the disposal.

Cleaning without taking the trap apart

If the nuts won't budge or you'd rather not open the pipe, try plunging first. InSinkErator's method for a kitchen sink (InSinkErator):

1. On a double sink, block the other drain with a stopper so the pressure doesn't escape.
2. Fill the sink with about 4 inches of water.
3. Put a sink plunger over the drain, press down slowly and gently, then pull up quickly. Repeat several times.
4. When the water drains, run water for a minute or two.

Plunging can push out a soft clog but won't scrub grease off the trap walls. If the smell returns within days, take the trap off and clean it.

Skip the harsh chemicals

Poison Control warns that many drain cleaners contain highly concentrated acidic or alkaline chemicals that must be used with great caution, and that swallowing them can cause serious burns (Poison Control). Never open a trap that has drain cleaner in it. Cleaning the trap by hand is safer and works better on a smell.

If you do use a drain cleaner on a different job, Poison Control says to wear goggles and rubber gloves, pour carefully and close to the drain to avoid splashing, and keep the container closed and out of children's reach (Poison Control).

How to keep the trap from smelling again

• Wipe pans before washing. Seattle says small amounts of cooled grease can be wiped up with paper towels and put in the compost, and larger amounts scraped into a lidded container for the garbage (Seattle Public Utilities).
• Use a sink strainer and empty it into the compost or trash (Seattle Public Utilities).
• Run cold water with the disposal. InSinkErator says to run a moderate flow of cold water while grinding and for a few seconds after, and to avoid hot water while grinding (InSinkErator).
• Never pour grease or fat into the disposal or drain (InSinkErator).
• Clean the disposal baffle every so often, using the steps above.

If the smell is still there

• The trap leaks. A slow drip into the cabinet means the water seal may be dropping. Reseat the washers.
• The sink is rarely used. North Royalton says normal use keeps traps full and recommends running water through drains that aren't used often (North Royalton).
• The smell is sewer gas, not food. If several drains smell even with clean, full traps, have a plumber check the drain lines and vents.

If the sink is also slow on both sides, see both sides of a kitchen sink draining slowly. If the same smell is coming from a basement drain, our guide to a basement floor drain sewer smell covers dry traps and cleanout plugs.