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How to unblock a sink
A sink that drains slowly is nearly always blocked by grease, food, hair or soap scum in the trap just below it. You can clear most blockages with a plunger and a bucket.
Start simple: boiling-hot water is not always the answer
For a kitchen sink with a greasy slow drain, run hot tap water for a minute. Be careful with kettles of boiling water: it can soften plastic pipes and crack some ceramic sinks. Hot tap water is safer and often enough for light grease.
Plunger method
- Remove the plug and clear any visible debris. Block the overflow hole with a damp cloth so pressure goes down the pipe.
- Fill the sink with a few centimetres of water so the plunger cup is covered.
- Press the plunger firmly over the plughole and pump up and down about ten times with a good seal.
- Pull it away sharply. If water drains, run the hot tap for a couple of minutes.
Use a sink plunger (flat cup), not the type for toilets, and use one that is kept for sinks only.
Clean the trap (U-bend)
The curved pipe under the sink holds water to stop smells and traps debris.
- Put a bucket under the trap and lay towels around it.
- Unscrew the plastic nuts by hand, or with a wrench if tight. Take care with old, brittle plastic.
- Empty the contents into the bucket, wear rubber gloves, and clean inside with an old brush.
- Refit the trap, making sure the washers sit flat, and hand-tighten. Run water to check for leaks.
If the trap is clear
Try a drain snake or drain auger fed in through the trap pipe. If the blockage lies further down, a plumber or your water company may be involved. Blocked shared drains outside the property can be the responsibility of the water company, depending on where the pipe is. Check with your supplier.
A note on drain chemicals
Caustic drain cleaners can be dangerous: they can burn skin and eyes, damage some pipes, and produce dangerous reactions if mixed with other products. Never mix cleaning products. If you do use one, follow the label and ventilate. Mechanical methods (plunger, trap, snake) are safer. Bicarbonate of soda and vinegar will fizz, but often won't shift a real blockage.
Prevent blockages
- Never pour cooking fat or oil down the sink. Let it set in a container and bin it.
- Use a plughole strainer in the kitchen and bathroom to catch food and hair.
- Do not flush wipes, even those labelled as flushable.
- Flush through with hot water and a little washing-up liquid now and then.
If several drains in the house are slow at once, the problem is likely further along, and it is time to call a drainage specialist. See also fixing a dripping tap and our basic toolkit.
Bathroom basins and baths
Bathroom blockages are usually hair bound with soap. Many pop-up plugs lift out or unscrew, and you can pull the hair out with a bent wire or a cheap plastic drain tool. Wear gloves. Baths and showers often have a small grille with a screw; remove it and clean under it. Rinse with hot water afterwards. If water backs up from the bath into the basin, or a toilet gurgles when you run a tap, the main drain may be affected, and you should call a drainage company or your water company for advice.
Frequently asked questions
Can I use boiling water on a blocked sink?
Use very hot tap water first. Boiling water can damage some plastic pipes and cracked ceramic, so be careful.
Are drain unblocker chemicals safe?
They can be hazardous. Follow the label exactly, wear gloves and eye protection, and never mix products. Mechanical methods are safer for most people.
When should I call a plumber?
When the trap is clear and the sink is still blocked, when several drains are slow, or if you smell sewage.