Quick answer
Kitchen sinks usually clog from grease, food scraps, or a jammed disposal, and sometimes from a blocked dishwasher drain connection. Try a plunger, then clean the trap. Avoid chemical drain cleaners. If other drains are slow or water backs up in a tub or toilet when you use the sink, the blockage is likely in the main line.
Why kitchen sinks clog
Kitchen sink drains carry grease, food scraps, and residue along with the water.
Grease is the biggest offender. The City of Edmonds, in Snohomish County, explains that fats, oils, and grease mostly enter drains when people rinse dishes or wash pots and pans without wiping them first. The grease cools and sticks to the pipe. The buildup can cause blockages and backups into homes.
Food scraps add to the problem. The City of Bellevue's guidance lists food items, coffee grounds, and eggshells among the things that should not go down drains. The City of Bellingham notes that scraps can still cause trouble after they have gone through a garbage disposal, and that a disposal does not make them safe to send down the drain.
Garbage disposal problems
If your sink has a disposal, it can be the source of the clog.
InSinkErator, a disposal manufacturer, says never to put fats, oils, or grease in a disposal or down the sink drain. It also recommends adding food in smaller batches and running a strong flow of cold water while grinding. Coffee grounds and eggshells are not harmful to the unit itself, the company says, but a lot at once can cause clogs or slow drains, especially in older plumbing.
The City of Edmonds goes further and advises residents to stop using in-sink disposals for food, since they can send grease into the sewer.
Safety first with a disposal
Never put your hand into a garbage disposal. InSinkErator's operating instructions state not to put hands into the disposer while it is operating, and that the unit should be switched off or unplugged before you try to free a jammed rotor with a tool.
If the disposal hums but does not spin, follow this order.
- Turn the disposal switch off, then unplug it or turn off its power at the breaker.
- Use the wrench your manufacturer specifies. InSinkErator describes inserting a dejamming wrench through the sink opening and twisting it back and forth until the shredder turns freely.
- If it makes no sound at all, let it cool for 3 to 5 minutes, then press the red reset button on the bottom. Do not strike the reset button.
A shared drain: double basins and the dishwasher
Many kitchens have a double basin. Family Handyman's advice is to block the other drain with a wet rag or the basket strainer before plunging a double sink.
The dishwasher drain also ties into the sink drain or disposal. Family Handyman recommends clamping the flexible dishwasher drain line before plunging, so dirty water cannot flow back into the cabinet.
If dirty water appears in your dishwasher, an appliance parts resource explains that dishwasher drain hoses are routed up in a high loop, near the underside of the countertop, to prevent dirty water from flowing back in, and that some local codes call for an air gap instead. Debris inside the hose can also cause poor drainage.
Try a plunger first
Use a cup plunger, the dome-shaped type for flat drains such as sinks and tubs. A flange plunger is for toilets. This Old House describes the sink technique below, and Family Handyman adds the details on water depth and timing.
- Remove the stopper if there is one, and cover the overflow hole with a wet cloth.
- Fill the sink with 3 to 4 inches of water so the plunger can seal.
- If it is a double sink, block the other drain with a wet rag or the strainer.
- Place the plunger over the drain and plunge vigorously for about 20 seconds.
- On the last upstroke, pull the plunger off. If the water does not drain straight down, keep plunging for several minutes.
- Run water to check that the clog is gone.
Clean out the trap
If plunging does not work, the clog may be in the P-trap, the curved pipe under the sink. Here is the process Family Handyman describes.
- Sponge out any standing water and set a bucket under the trap.
- Loosen the slip nuts, using pliers if needed, and remove the trap.
- Clean out debris and check the trap for cracks. Replace it if it is worn.
- Reinstall it, tightening the nuts hand-tight plus a quarter turn.
- Test with warm water and check for drips.
If the trap is clear
If the trap is clean and the sink still drains slowly, the clog may be in the trap arm, the pipe running into the wall. Family Handyman says to loosen the slip nut, remove the trap arm, and clear debris from the pipe opening.
A drain snake can reach further. The same guide describes pulling out 6 to 10 inches of cable, feeding it into the drain while turning the crank clockwise, and continuing until the tip breaks through the clog.
What not to do
Skip chemical drain cleaners if you can. The Poison Control center says strong alkali drain cleaners are very caustic and can cause chemical burns on the skin and in the lungs, and that lye can cause severe eye injuries. It warns against ever mixing household cleaning products because of poisonous fumes. HomeTips adds that chemical cleaners are usually ineffective on main line clogs and can damage pipes.
If you have already poured a cleaner into the drain, tell anyone who works on it before the trap is opened.
- Do not pour grease down the drain. Let cooled fat solidify in a container and put it in the trash. This is the advice from Bellevue and Edmonds.
- Do not rely on hot water or soap to carry grease away. Edmonds notes in its business guidance that hot water, detergent, and degreasers do not keep grease from sticking in pipes.
- Do not put your hand in the disposal, even to grab a dropped item.
- Do not plunge a sink that has caustic cleaner standing in it. Poison Control describes a child splashed in the face by lye drain cleaner poured into a sink of water.
Prevention that actually helps
A few habits reduce the odds of a repeat clog. Wipe greasy dishes with a paper towel and throw it away before washing. Use a sink strainer to catch food waste. Scrape plates into the trash or yard waste cart rather than the sink. Edmonds and Bellevue recommend these steps.
When it is the main line
Not every clog is in the kitchen. HomeTips says that when only one fixture is slow, the clog is likely local. If several are affected, the problem is likely in the main drain or sewer line.
Signs of a main line clog include multiple slow drains, gurgling toilets when other fixtures run, water backing up in tubs, showers, or toilets, sewage odors, and standing water near floor drains. If running the kitchen sink brings water up in a tub or floor drain, treat it as a main line problem.
HomeTips advises cutting back water use at once: avoid running sinks or showers, limit toilet use, and skip the washing machine. Pierce County, Washington, and the City of Bellevue both state that the private sewer pipe is the homeowner's responsibility, so check with your own utility about where its responsibility ends.
When to call Pyper Plumbing
Call a plumber when the plunger and trap cleaning have not cleared the drain, when the clog keeps coming back, when other fixtures are affected, or when you smell sewage. Call right away if water is flooding the floor.
Pyper Plumbing provides drain cleaning, garbage disposal repair and replacement, sewer line repair, and emergency plumbing repair across Snohomish, Skagit, Whatcom, and Island counties. If you are on a septic system, Pyper does not do septic work, so a septic contractor should be called for that problem.
Common questions
Why does my kitchen sink keep clogging?
Grease and food scraps are the most common causes. The City of Edmonds says grease enters drains when pots and pans are rinsed without wiping them first, then cools and sticks to the pipe. Wiping dishes and using a sink strainer helps.
Is it safe to put my hand in the garbage disposal to remove a clog?
No. InSinkErator instructs that hands should not go into a disposer while it is operating, and that it should be switched off or unplugged before freeing a jam with a tool. Keep hands out and use tools.
Should I use chemical drain cleaner on a kitchen sink?
It is best avoided. Poison Control describes strong alkali drain cleaners as very caustic, capable of chemical burns, and warns never to mix cleaners. Start with a plunger and trap cleaning.
How do I know if the clog is in the main line instead of the sink?
If several fixtures drain slowly, gurgle, or back up together, the main line is the likely cause. A kitchen sink that is slow while everything else drains normally is more likely a local clog.
Sources
Facts in this guide come from the following references. Local rules and manufacturer instructions can differ, so follow your utility and your equipment manual.
- City of Edmonds: Fats, Oils & Grease
- City of Bellingham: Keep Our Pipes Clear
- City of Bellevue: Preventing Sewer Backups
- Pierce County, WA: Wipes Clog Pipes
- InSinkErator: What Not to Put in a Garbage Disposal
- InSinkErator: Disposer Operating Instructions
- Family Handyman: How to Clean and Unclog a Kitchen Sink Drain
- This Old House: How to Use a Plunger
- Appliance Parts Pros: What Is a Dishwasher High Loop
- HomeTips: Sewer Line Clog Signs
- HomeTips: Drain and Sewer Problems
- Poison Control: Spring Cleaning
This guide is general information, not a substitute for an on-site inspection. If you smell natural gas, leave the building and call 911 or your gas utility. Pyper does not perform gas line work.
