Sink Gurgling? What It Means and How to Stop It

A gurgling sink means air is being pushed or pulled through the water in the trap because it can't move freely through the waste pipe. If the sink gurgles as it drains and empties slowly, the usual cause is a partial blockage of grease, food or hair in the trap or the pipe beyond it. If it gurgles when something else drains, like the washing machine, dishwasher, bath or toilet, the likely cause is a venting problem or a partial blockage in a pipe the fittings share. When several sinks and the toilet gurgle together, look at the outside drain. Working out which of these you have takes a few minutes, and it decides whether the fix is a trap you can clean yourself or a job for a plumber.

Why a sink gurgles

Under every sink there is a trap: the U-shaped or bottle-shaped fitting that holds a small amount of water to stop drain smells coming up the plughole. As water drains, it has to push air ahead of it down the pipe, and air has to get in behind it. If the pipe is narrowed by a blockage, or air can't get in where it should, the air forces its way back through the water in the trap instead. That's the gurgle.

Approved Document H, the Building Regulations guidance on drainage, expects traps to keep a water seal (usually 75mm deep on sinks and basins) and waste pipes to be sized, sloped and ventilated so that seal isn't pulled out when water runs through. A gurgling sink is a sign that one of those things isn't working as it should.

Blockage or venting? How to tell

Partial blockages

In kitchens, grease and food scraps are the usual cause. Fat goes down the sink warm, cools in the pipe and coats the inside, and food catches on it until the pipe narrows. In bathrooms it's hair and soap, usually in the trap or just past it. The sink still drains, just slowly, and gurgles because water and air are fighting for the same narrow gap.

These are the most common cause of a gurgling sink, and often the easiest to sort. Clearing the trap by hand, then flushing the pipe with hot water, usually cures it. If the blockage is further along the pipe, a plumber can clear it with a drain snake or by opening an access point. Our guides to a blocked kitchen sink and a blocked bathroom sink go through the steps.

Venting and siphoning problems

If the sink drains normally but gurgles when something else empties, the problem is usually air, not a blockage in the sink itself.

• Shared waste pipes. In most kitchens the washing machine and dishwasher drain into the same pipe as the sink. When they pump out, the surge pushes air ahead of it and pulls water out of the sink trap behind it. If that shared pipe is partly lined with grease and lint, it's much worse. Our guide to a washing machine not draining covers the shared waste in more detail.
• A failed air admittance valve. Many homes, especially flats and extensions, don't have a pipe venting through the roof for every waste run. Instead they have an air admittance valve, a one-way valve that lets air into the pipe when water rushes down and closes to keep smells in. They are often hidden in boxing, under the sink or in a cupboard. If one sticks shut, the fittings on that pipe gurgle. If it sticks open, you may smell drains.
• A long or steep waste run. If a sink or basin waste runs a long way, or drops too steeply, water running down it can pull the trap empty behind it. Building Regulations guidance limits how long and how steep a basin or sink waste can run before it needs extra venting or a different trap. This is common after a kitchen or bathroom has been moved, and the fix is a change to the pipework or trap.
• The soil stack. If sinks gurgle when the toilet flushes, the main soil stack may be partly blocked or its vent at the top (often a pipe above the roofline) may be blocked by leaves or a nest.

A trap that keeps getting sucked dry lets sewer gas into the room. If your gurgling sink also smells, see our guide to a kitchen sink that smells of sewage. The same problem in the toilet is covered in our guide to a gurgling toilet.

What you can check yourself

1. Clean the trap. Put a bowl underneath, unscrew the trap by hand and clear out what's inside. Check the rubber washers are seated properly when you put it back, then run water and check for drips.
2. Plunge it properly. Use a sink plunger with a little water in the bowl. Block the overflow hole with a damp cloth, and on a double sink block the other plughole too, or the pressure just escapes.
3. Flush with hot water and washing-up liquid to shift grease. Avoid pouring boiling water into plastic waste pipes repeatedly.
4. Find the air admittance valve if you have one. It usually looks like a small grey or white cap on top of a vertical pipe. Most push on. If the gurgling stops when you lift it off briefly while the water runs, the valve is probably sticking and needs replacing. Put it straight back, because the open pipe lets drain smells out.
5. Check the outside gully where the kitchen waste pipe discharges. If it's full of water, grease or leaves, the blockage is outside, and our guide to a blocked outside drain will help.

Chemical drain cleaners rarely fix gurgling. They don't touch venting problems or blockages further down, and repeated use can damage plastic traps and seals.

When to call a plumber

Call a plumber if the gurgling comes back after you've cleaned the trap, if the sink gurgles whenever another appliance drains, if several fittings gurgle or drain slowly at once, if you can smell drains, or if the kitchen or bathroom was recently refitted and the gurgling started afterwards. A partial blockage tends to get worse until the sink backs up, so it's cheaper to deal with it while water still goes down.

We charge £95 an hour for labour, plus a £60 call-out that's waived when the job runs over 2 hours. Parts are extra and we confirm the price before any work starts. Our blocked sink and blocked drain services cover London homes and flats, and the pricing page explains how jobs are charged.

Frequently Asked Questions