How do I unblock a sink?

Almost every sink blockage sits in one of three places: the plughole grating, the trap directly under the sink, or the horizontal pipe running to the soil stack. You work through them in that order because each is progressively more effort, and because the first two account for the large majority of blockages. Kitchen sinks block with congealed fat and food; bathroom sinks block with hair and soap.

Safety

What you'll need

• Sink plunger (the flat cup type)
• Bucket and old towels
• Rubber gloves
• Drain snake or flexible plastic hook (optional)
• Adjustable grips for tight trap nuts (optional)

Step by step

1. Clear the plughole grating of visible hair and debris first.In a bathroom sink this alone fixes it more often than people expect.
2. Block the overflow hole with a wet cloth.Without this the plunger just pushes air out of the overflow and does nothing.
3. Run enough water to cover the plunger cup, then plunge firmly 10–15 times.You need water, not air — water is incompressible and transmits the shock to the blockage.
4. If it clears, run hot water for a minute to flush what's loosened.Partly loosened debris re-settles a metre further along if you don't flush it through.
5. If it doesn't clear, put a bucket under the trap and unscrew the two collars by hand.They're usually plastic and hand-tight. Grips only if genuinely seized — plastic threads strip easily.
6. Empty and clean the trap out, then check the pipe openings either side of it.Expect grey sludge in a kitchen sink and a hair mat in a bathroom one.
7. If the trap was clear, feed a drain snake into the wall-side pipe and turn it as you push.Turning is what lets it work past bends. Pushing alone just jams it.
8. Reassemble the trap, hand tight, and run water while looking underneath for drips.Check the washers are seated flat and the right way round before tightening.

Tips

• Prevention: pour fat into a jar and bin it rather than down the sink, and fit a plughole hair catcher in the bathroom. Both cost almost nothing and prevent nearly all repeat blockages.
• A kettle of hot — not boiling — water with washing-up liquid will clear light grease build-up before it becomes a blockage. Boiling water can deform plastic traps and damage some pipe joints.
• Bicarbonate of soda followed by vinegar is a mild, safe maintenance flush. It won't shift an established blockage, whatever the internet says.
• If every drain in the house is slow at once, the problem is the shared soil stack or the drain outside, not the sink. That's a different job.

Common mistakes

• Reaching for chemical drain cleaner first — It's caustic, often doesn't clear solid blockages, and leaves a hazardous liquid sitting in the pipe for whoever opens it next.
• Plunging without blocking the overflow — The pressure escapes through the overflow and nothing happens.
• Overtightening plastic trap collars — Strips the thread or cracks the collar, turning a blockage into a leak.
• Pouring boiling water into a plastic trap — It can soften and distort the fittings. Hot from the tap is plenty.

Questions people ask