Sink blocked? How to clear the drain

The drain of a bathroom basin is narrow and has to deal with a mixture of hair, soap, toothpaste, shaving foam and skin oils every day. Each of these substances isn't too bad on its own, but together they form a tough, grey sludge that gets stuck around the plug and in the bend of the trap. It happens gradually: first the basin drains a bit more slowly, then a layer of water remains, and eventually it barely drains at all.

Where is the blockage usually located?

• Around the pop-up plug. Many washbasins have a plug that you open and close with a lever behind the tap or by pressing on it. Hair catches on the rod and mechanism of such a plug, to which soap then adheres. It is the most common place for a blockage.
• In the trap. Under the basin there is a curved pipe or a bottle trap (a round pot). Some water always remains in it, so that no sewer odours can enter. Dirt also settles in that water, and over time a layer of sludge forms there.
• In the overflow. The hole at the top of the basin drains water if the bowl gets too full. Soap scum can build up there too, which mainly causes a musty smell.
• In the pipe behind the trap. Less common, but it does happen that the blockage is in the section of pipe in the wall, for example with older pipes with limescale or insufficient fall.

Check first

Run water in the shower and flush the toilet. If they drain normally, the problem is almost certainly in the sink itself. If you notice water coming up in the shower drain when the sink empties, or the toilet gurgles, the blockage is further down in the shared drain. In that case, first read what it means when water comes up in the shower, because cleaning the sink won't help.

Unblocking a basin: step-by-step plan

1. Remove the plug. With many pop-up plugs, you can pull the plug upwards or turn it a quarter turn and lift it out. If it's stuck, look under the sink: there's a rod with a clip or nut that operates the mechanism. Unscrew it and the plug will come free. Wipe off the hair and dirt with an old cloth.
2. Fish out the top blockage. With a plastic hair snake (a narrow strip with hooks, available at DIY stores) you can remove hair from the upper part of the drain. Often the sink will drain properly again after this step.
3. Use a plunger. Hold a wet cloth firmly against the overflow, otherwise the pressure will escape there. Leave a few centimetres of water in the basin, place a small plunger straight over the drain and pump vigorously up and down several times.
4. Clean the trap. Place a bucket under the washbasin and have a towel ready. For a bottle trap, unscrew the two compression nuts by hand; for a tubular trap, unscrew the bottom section. Rinse everything out into the bucket, not into the same washbasin. Check that the rubber seals are still intact and hand-tighten everything back in place.
5. Work with a hand snake. If it still drains slowly afterwards, the blockage is in the pipe in the wall. Feed a thin hand snake into the wall opening whilst turning, without forcing. Pull it back, remove the dirt and rinse thoroughly with plenty of warm water.
6. Test for leaks. Let the basin fill halfway and pull the plug. Use a torch to check whether the connections under the basin remain dry.

What you'd better not do

• No chemical drain cleaner. These products are corrosive, damage rubber seals and sealant and remain if the blockage doesn't dissolve. Anyone who then unscrews the trap gets that stuff on their hands. You can read more about this in drain unblockers: what works and what doesn't.
• No boiling water. Sink traps and drain pipes are usually plastic. Boiling water can deform PVC over time, causing joints to leak. Warm tap water is sufficient.
• Don't poke with wire or a knitting needle. This pushes the hair deeper into the pipe and damages the plug mechanism.
• Don't overtighten the trap with pliers. Plastic nuts will then crack or the ring will sit crooked. Hand-tight is enough.

How to prevent a new blockage

• Remove the pop-up plug every few weeks and wipe the hair off it. It takes a minute and prevents most problems.
• Don't brush or comb your hair over the open drain, or close the plug for a moment and throw the hair in the general waste afterwards.
• After brushing your teeth and shaving, rinse briefly with warm water so that toothpaste and foam don't settle in the trap.
• Once a week, let the washbasin fill with hot water for half a minute, then pull the plug. The flow will carry away loose debris.
• Don't throw cotton buds, hair ties or make-up remnants down the basin.

More general tips for all drains in the house can be found in the article preventing blockages.

Does the basin smell but does it drain?

A nasty smell from the basin is often caused by build-up in the overflow or a trap that has dried out, for example in a guest bathroom that's rarely used. Simply run the water for a moment. If the smell persists, read more about sewer smell in the house.

Unsure whether to continue yourself? In unblock yourself or call the plumber we set out the considerations. If the kitchen is also draining poorly, see kitchen sink blocked. For drain unblocking in The Hague and Delft region you can visit our page on drain unblocking.