Blocked sink or basin: how to unblock it without chemicals

No chemicals needed. Start with the plunger.

The answer in 2 lines. A blocked sink or basin is nearly always blocked close to the plughole or in the U-bend trap underneath: fat and food scraps in the kitchen, hair and soap in the bathroom. Start with a sink plunger, then unscrew and clean the trap, and only then use a drain snake. Skip the caustic drain unblockers: they can burn skin and eyes, and they don't always shift the blockage. If several drains are slow or water comes back up elsewhere, the problem is further down: call your landlord, a drainage engineer, or your water company if the drain is shared.

The first 3 steps

Stop running water into it: there is no point filling the sink further.
Check the other drains: if only this sink is slow, the blockage is close by; if the bath, shower or toilet also drain slowly or gurgle, it is further down the pipe.
Remove what you can see: the plug strainer, hair, food scraps, wearing rubber gloves.

Stop: danger

If a chemical drain unblocker has already gone in, don't plunge and don't open the trap: the water can splash and burn your skin or eyes. Ventilate, wait, and tell the plumber which product you used.
Never mix a drain unblocker with bleach or another cleaner: some mixtures give off toxic gas. In the eyes: rinse with plenty of clean running water for at least 10 minutes and get medical help. Swallowed, or someone unwell: call NHS 111, or 999 in an emergency, and keep the bottle to show them.

The steps, simplest first

1. Plunger: a few centimetres of water in the sink, block the overflow hole with a wet cloth (and the second plughole on a double sink), then firm pushes and pulls. For a blockage near the plughole.
2. The trap (U-bend): bucket underneath, unscrew it by hand, empty it, clean it, screw it back. For hair, grease, a small object dropped in.
3. Drain snake (a flexible cable you turn with a handle): fed into the pipe once the trap is off. For a blockage further along the waste pipe.
4. Plumber or drainage engineer: the blockage won't shift, or several drains are affected.

Choosing a plunger: for a sink or basin, a small cup plunger without a flange; the flanged kind is for toilets. A basic plastic drain snake (often called a drain unblocker or hair snake) is enough for a basin. Which? explains how to unblock a sink and what never to pour down it: Which? — How to unblock a sink.

Cleaning the trap, step by step

Put a bucket or bowl under the trap (the bend under the sink or basin) and keep a cloth to hand.
Unscrew the nuts by hand. On a basin, the trap is sometimes a bottle trap whose bottom part unscrews.
Empty it, pull out hair and gunk, scrub it in hot water with an old brush.
Check the rubber washers: a squashed or split one is replaced with the same size.
Screw it back by hand, run the water and look for drips.

What not to do

Pouring boiling water into a blocked sink: it can damage plastic pipes and seals. Hot tap water is enough.
Poking a wire coat hanger down: it scratches the plughole and can puncture a pipe.
Using several different drain unblockers one after another "to be sure".

Home remedies: what to expect

Bicarbonate of soda then white vinegar, followed by hot water: the fizzing may help with light build-up or as upkeep. On a real blockage, it doesn't replace the plunger or cleaning the trap.
Hot water and washing-up liquid: useful when it's grease setting in a kitchen waste pipe.
Enzyme drain cleaners: slow-acting, better for upkeep than for an emergency. Read the label.

Good to know

Cooking fat, oil and grease don't go down the sink: they set hard in the pipes and help form "fatbergs" in the sewers. Water companies' advice: let it cool, scrape it into the bin, wipe greasy pans with kitchen paper.
A sink strainer in the kitchen and a hair catcher in the basin or shower stop most blockages. Measure your plughole before buying.

Who pays and who to call

If you rent: in England, the landlord must keep basins, sinks, baths and drains in repair (Landlord and Tenant Act 1985, section 11). But a blockage you caused, with food or hair, is often expected to be cleared by the tenant. If it comes from the installation itself (a poorly laid or damaged pipe), tell your landlord in writing.
Flats and shared drains: if water comes back up in several homes, the shared drain or sewer is blocked. Since 1 October 2011, in England and Wales, sewers shared with neighbours, and the part of your own drain that lies outside your property boundary, belong to your water and sewerage company, which clears blockages in them at no cost to you. The pipe serving only your home, inside your boundary, stays your responsibility (or your landlord's).
Plumber: WaterSafe lists approved plumbers by postcode (WaterSafe — Finding a plumber): check they are approved, and ask for a price before they start.

In your city: your sewerage company

London: Thames Water.
Birmingham: Severn Trent.
Manchester and Liverpool: United Utilities.
Leeds and Sheffield: Yorkshire Water.
Newcastle: Northumbrian Water.
Bristol: Wessex Water for sewerage (your tap water comes from Bristol Water).
These are the companies for most of each city. Your water bill shows which company handles your sewerage.

In Nottingham, Grace notices her bathroom basin draining more and more slowly. She puts a bowl underneath, unscrews the bottle trap by hand and pulls out a clump of hair and soap. After a rinse in hot water, the basin drains in seconds. She now uses a small hair catcher over the plughole.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 1 November 2026, for England. Confidence: high for the steps and the safety warnings on chemical unblockers (Which?, St John Ambulance); high for the 2011 transfer of shared sewers and for section 11; medium for who pays for a blockage in a rented home, which depends on the cause and your tenancy agreement. We found no official statistics on blocked household sinks, so we don't quote one. This guide describes common cases, not a diagnosis.