A slow or blocked sink is usually a lump of grease, food or hair sitting just out of sight. You can clear the vast majority yourself, and you should try before reaching for harsh drain chemicals.

Work through these in order

  1. Boiling water. For grease blockages, a kettle of boiling water down the drain often does it (skip this on PVC/plastic pipes — use hot tap water).
  2. Plunger. Block the overflow hole with a wet cloth, then plunge firmly a dozen times.
  3. Baking soda + vinegar. Half a cup of each, leave 15 minutes, flush with hot water.
  4. Clear the trap. Put a bucket under the U-bend, unscrew it, empty the gunk, reattach.
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Go easy on chemical drain cleaners

They're harsh on pipes and dangerous if they don't clear — you don't want caustic water sitting in a sink you then have to bail out. Try the mechanical methods first.

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Prevent the next one

Never pour cooking grease down the drain — let it solidify and bin it. Use a sink strainer to catch food and hair.

Mistakes that make a blockage worse

Half the time a sink stays blocked because of something you did while trying to clear it. A few habits turn a ten-minute job into a real headache:

  • Pouring shop-bought caustic drain cleaner in first. If it doesn't shift the clog, you now have a pipe full of corrosive liquid — you can't plunge or open the trap safely, so you're stuck waiting or calling someone.
  • Plunging a sink with the overflow open. The pressure escapes out of the little overflow hole instead of hitting the blockage. Block it with a wet cloth held firmly, then plunge.
  • Boiling water down a plastic waste pipe or over ceramic. Very hot water can soften plastic joints and, rarely, crack cold ceramic. Use hot-tap water for plastic; save the kettle for metal traps.
  • Removing the U-bend without a bucket underneath. There's always standing water in there. Every time.

A worked example: the classic kitchen grease clog

Say your kitchen sink drains slowly and smells faintly of old cooking. That's almost always fat and food building up in the trap. Here's the realistic run-through: bail out the standing water so you're not working blind, then pour a kettle of hot (not boiling) water with a good squirt of washing-up liquid down and wait five minutes — the detergent breaks down grease. Plunge fifteen to twenty firm strokes with the overflow blocked. If it's still slow, put a bucket under the U-bend, unscrew it by hand, and scoop out the grey sludge. Total time is usually fifteen to twenty minutes and it costs you nothing but a pair of rubber gloves.

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How to know it actually worked

Fill the sink to the top, then pull the plug. A properly cleared drain empties fast with a strong glug and a little whirlpool. If it drains in a slow, quiet trickle, the clog has only partly shifted — go again before you put everything back.

When to stop and call a plumber

Most single blocked sinks are yours to fix. But some signs point to a problem further down the system that a plunger won't touch:

  • More than one fixture backing up at once — sink, toilet and bath all sluggish means the main drain, not your trap.
  • Water coming back up in a different appliance when you run the tap or flush.
  • You've cleared the trap and it's still blocked — the clog is beyond the U-bend, out of easy reach.
  • Gurgling from other drains or a persistent sewage smell around the house.
Written by Niharika Parashar

Frequently asked questions

Can I use baking soda and vinegar to unblock a sink?
It helps with light grease and smells, not solid blockages. Tip in half a cup of bicarb, then the same of white vinegar, cover the plughole for ten minutes while it fizzes, and flush with hot water. Treat it as a gentle maintenance flush rather than a fix for a fully blocked sink — for that, a plunger or clearing the trap works far better.
Is it safe to leave a blocked sink overnight?
Yes, standing water alone won't damage anything, though it may start to smell. The one thing to avoid is leaving shop-bought caustic drain cleaner sitting in there overnight — it's corrosive and makes plunging or opening the trap dangerous the next morning. If you've used chemicals and they haven't worked, that's the point to stop and call someone rather than wait.
Why does my sink gurgle but still drain slowly?
Gurgling is air struggling past a partial blockage or a venting issue. If it's just that one sink, a partly clogged trap is the likely cause — clear it and the noise usually goes. If several drains gurgle together, or it happens when you use another appliance, the problem is further down the main drain and worth getting looked at properly.
How do I stop the sink blocking again?
Never pour fat or oil down it — let it set and bin it. Fit a cheap plughole strainer to catch food and hair. Once a week, run the hot tap for thirty seconds after washing up to keep grease moving. For bathroom sinks, pull out the trapped hair around the plug every so often before it builds into a proper clog.

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