How to Unblock a Kitchen Sink Without Calling Anyone
Clear a slow or blocked kitchen sink using hot water, a plunger and the trap, with advice on what to avoid and when a plumber is the better call.
Standing water in the sink is one of the most common household plumbing complaints. In a kitchen the cause is nearly always the same: grease, food scraps and soap residue building up in the waste pipe and trap. That is good news, because the fix is usually simple, cheap and does not need chemicals.
Why kitchen sinks block
Cooking fat cools and sticks to the pipe walls. Coffee grounds, rice and pasta swell and pack the trap. Over weeks, the pipe narrows until water barely moves. A gurgling sound as the sink empties is an early sign.
Method one: hot water and washing-up liquid
For a slow drain that is not fully blocked:
- Boil a kettle and let it cool for a minute. Boiling water straight into some plastic waste pipes or a ceramic sink is not ideal, so very hot rather than boiling is safer.
- Squirt a good amount of washing-up liquid down the plughole.
- Pour the hot water slowly.
- Wait a few minutes and repeat if it helps.
This can break up soft grease deposits.
Method two: plunge it properly
- Fill the sink with a few centimetres of water so the plunger cup is submerged.
- If there is a double sink, block the other plughole with a wet cloth. If there is an overflow, hold a damp cloth over it.
- Place the plunger over the plug and push down and pull up steadily about ten or fifteen times.
- Pull away sharply and see if the water drains.
Use a flat-bottomed sink plunger rather than a toilet one if you have it.
Method three: clean the trap
If plunging fails, the blockage is probably in the U-bend.
- Put a bucket under the trap. Expect a lot of grim water.
- Unscrew the large nuts at each end of the trap by hand. If stiff, use a cloth and spanner gently.
- Empty the contents into the bucket and clear the gunk with a bottle brush.
- Check the pipe leading to the wall with a torch, and clear any visible blockage.
- Refit the trap, making sure the washers sit squarely, then run the water and check for leaks.
If it leaks, see our guide on a leak under the sink.
Method four: a drain auger
A small hand auger, sometimes called a drain snake, reaches further than a plunger. Feed it into the waste pipe, turn the handle so it catches the blockage, and then withdraw it. Be gentle with older plastic pipes.
What to avoid
- Strong chemical drain cleaners. They can damage pipes and seals, can be unpleasant to handle, and leave a hazardous standing liquid if they fail. Plumbers have to work with whatever is left behind.
- Forcing metal tools in blindly. You can puncture a pipe.
- Pouring fat down the drain. Let it cool and bin it.
- Running the tap flat out on a half-blocked sink. It will overflow.
Keeping it clear
- Scrape plates into the bin.
- Use a sink strainer.
- Flush with hot water and washing-up liquid occasionally.
- Wipe greasy pans with kitchen roll before washing.
When to call a plumber
Get help if:
- more than one fixture is draining slowly, which suggests a main drain issue;
- the blockage keeps returning;
- you hear gurgling from other drains or smell sewage;
- you cannot access the trap, or the trap is fixed;
- the sink overflows into the cupboard.
You can see what to expect in the cost of unblocking a drain.
Worked example: a Sunday evening block
After a roast dinner the sink is full of greasy water and does not move. The householder tries the hot water and washing-up liquid method first, which helps slightly but not enough. A plunger on the other hand, with the second plughole blocked with a wet cloth, gets the water moving. A few minutes later the sink drains but gurgles, so they put a bucket under the trap, unscrew it and find a thick plug of grease and rice. Cleaned out and refitted, the sink runs freely. Total cost: a bucket, a pair of gloves and about thirty minutes.
Choosing a method
| Symptom | Start with |
|---|---|
| Slow drain, gurgling | Hot water and washing-up liquid |
| Standing water, one sink | Plunger |
| Plunger fails | Clean the trap |
| Trap clear but still blocked | Hand auger |
| Other sinks and the bath also slow | Call a plumber about the main drain |
Mistakes people make
- Using a toilet plunger that does not seal properly.
- Forgetting to block the second bowl or overflow.
- Tightening trap nuts too hard and cracking plastic threads.
- Pouring chemicals first, then discovering the water is hazardous when the trap is removed.
- Not checking the dishwasher or washing machine waste, which may share the trap.
Special cases
- Waste disposal units. These need a different approach, and the manufacturer's instructions apply.
- Rentals. Blockages caused by misuse can be charged to the tenant, so photograph what you find.
- Flats. Persistent blockages across several flats are a building drain issue for the managing agent.
- Fitted units and cramped spaces. If you cannot reach the trap, ask a plumber rather than forcing it.
After the job
Run hot water for a minute, then check under the sink with tissue. Dispose of grease in the bin, not the toilet, and set a reminder to run hot water and detergent through the sink once a month.
Frequently asked questions
Does bicarbonate of soda and vinegar work?
It may help to freshen a drain and loosen light residue, but it rarely clears a proper blockage. Use it as a maintenance step, not a cure.
Can I use a toilet plunger on a sink?
It will work in a pinch, but a flat-bottomed plunger seals better on a sink.
Why does the sink drain slowly after being unblocked?
There may still be a partial blockage further down the pipe, or an undersized or poorly sloped waste. A plumber can check with a camera or rods.