How to Unblock a Sink: Kitchen & Bathroom UK Guide

Here’s the number that surprises most people: nine out of ten sink blockages in UK homes are caused by just two things, and they need almost opposite fixes. Kitchen sinks clog with grease, fat and food starch. Bathroom sinks clog with hair, soap scum and toothpaste. Pour caustic soda down a hair blockage and you’ll get a nasty chemical mess and a sink that’s still blocked. Use a plunger on a solid grease plug and you’ll just compress it further down the pipe.

Twenty years on the tools has taught me one thing above all: the fix has to match the cause, not the location of your sink alone, but what’s actually sitting in that trap. This guide splits how to unblock a sink into two separate playbooks, one for kitchens, one for bathrooms, so you stop guessing and start clearing.

Contents

• What You Will Need
• Step-by-Step Method: How to Unblock a Sink by Cause
• When to Stop and Call a Pro
• How to Prevent It Next Time

What You Will Need

Before you touch anything under the sink, gather your kit. Trying to unclog a sink UK-style with half the tools missing just means three trips to the garage in wet trousers.

• A sink plunger (cup-style, not the flanged toilet type)
• An old towel and a bucket – the U-bend will still hold water when you open it
• An adjustable spanner or slip-joint pliers
• A drain snake or flexible drain rod (a straightened wire coat hanger works in a pinch for hair)
• Rubber gloves
• Bicarbonate of soda and white vinegar
• A torch, because under-sink cupboards are never as well lit as you think

Step-by-Step Method: How to Unblock a Sink by Cause

This is the part most guides get wrong. They give you one method and hope it fits every sink in the country. It doesn’t. Work out which type you’ve got first, then follow that column.

Fix 1: Unblock Kitchen Sink Grease Blockages

Kitchen sinks fail slowly, over weeks, because fat coats the inside of the pipe like fur in a kettle. Every wash adds another thin layer until the gap closes.

1. Boil a full kettle and pour it down in three stages, thirty seconds apart, giving each round time to soften the fat.
2. Add 100g of bicarbonate of soda followed by 200ml of white vinegar. It’ll fizz. Leave it fifteen minutes.
3. Flush with more boiling water. If it drains freely, you’re done.
4. Still slow? Open the U-bend over a bucket with your spanner and you’ll likely find a solid yellow-grey plug sitting right at the bend. Scoop it out by hand into the bucket, don’t wash it further down the system.
5. Refit the U-bend, hand-tight plus a quarter turn, and run the tap for two minutes to check for leaks.

Fix 2: Blocked Bathroom Sink Fix for Hair and Soap Scum

Bathroom blockages sit differently. Hair wraps around the pop-up waste stopper and soap scum binds it into a solid mat, usually within the first fifteen centimetres of pipe. Heat and fizzing chemicals barely touch it.

1. Lift or unscrew the pop-up stopper first. On most UK basins it twists anticlockwise or has a small retaining nut underneath. Half of all “blocked” bathroom sinks clear the moment you pull this out, because the hair mat is wound straight round it.
2. Plunge properly. Block the overflow hole with a wet cloth (this is the step people skip, and it’s why plunging fails), add enough water to cover the plunger cup, then push down slowly and pull up sharply six or seven times.
3. Feed a drain snake 20-30cm into the waste pipe, twist, and pull. You will pull out something unpleasant. That’s the job.
4. Check the U-bend as a last resort using the same method as the kitchen fix, but expect a black sludge of hair and soap rather than fat.

If either method leaves you stuck, don’t keep escalating chemicals. Ring us via our contact page and we’ll talk you through what to try next, or come out and finish the job with proper drain rods.

A Real Job: Two Sinks, One Visit, Two Different Fixes

Called out to a semi in Reigate last spring. Same house, same morning, two blocked sinks. The kitchen sink had a grease plug the size of a fist sitting in the trap, four years of chip-pan fat by the look of it – cleared in twenty minutes with the U-bend removed and a hot flush. The en-suite basin next door was a hair and conditioner mat wound round the pop-up waste, no grease anywhere near it. Same visit, same toolbox, two completely different blockages. The householder had spent £15 on three different bottles of drain cleaner over a fortnight trying one product on both sinks. Neither worked, because neither was matched to the actual cause.

When to Stop and Call a Pro

There’s no medal for battling on with a coat hanger for two hours. Call it in when you see any of these:

• Water backs up in a different fixture – if flushing the toilet makes the bathroom sink gurgle or rise, the blockage is past the sink and into the shared drain, per Water UK guidance on shared drainage responsibility.
• You’ve already used a chemical drain cleaner – mixing it with further plunging or a snake risks splashback into your face and hands.
• The smell is sewage, not food or soap – that points to a vent or soil stack issue beyond the trap.
• You’ve opened the U-bend and it’s still not draining – the blockage is further down the branch pipe than DIY tools reach.
• Any pipework was fitted or altered recently – work should meet WRAS water fittings regulations, and a botched fix can void that.

Compare that against wider drain problems – if it’s not just the sink, our guide on how to unblock a drain covers the outside gullies and shared runs too. And if you’re weighing up whether to call someone at all, our breakdown of drain unblocking cost will tell you roughly what you’re looking at before an engineer even arrives.

Is It Safe to Use Chemical Drain Cleaner on Every Blockage?

No, and this trips people up constantly. Caustic-based cleaners can damage older chrome or brass traps, and they do very little against a solid hair mat because there’s no fat for the chemical to break down. Bicarbonate and vinegar is gentler and works on both sink types, which is why it’s step one above rather than a shop-bought caustic cleaner.

How Long Should Unblocking a Sink Take?

A grease-blocked kitchen sink with the U-bend approach usually takes 20-30 minutes start to finish. A hair-blocked bathroom sink is often faster, ten minutes, if the pop-up stopper is the culprit. If you’re past forty minutes with no change, that’s your natural stopping point.

How to Prevent It Next Time

Prevention splits by sink, same as the fix does.

For the kitchen: keep a fat jar by the hob for pan drippings instead of pouring them down the sink, run cold (not hot) water when scraping plates so fat doesn’t liquefy and coat the pipe, and fit a simple mesh strainer over the plughole to catch food scraps before they reach the trap.

For the bathroom: a cheap hair-catcher over the plughole stops the problem before it starts, and it’s worth pulling the pop-up stopper out and giving it a wipe once a month rather than waiting for a full block. The Chartered Institute of Plumbing and Heating Engineering (CIPHE) lists exactly this kind of routine maintenance as the biggest single factor in avoiding emergency callouts.

Landlords and letting agents managing multiple properties see this pattern constantly across a portfolio – it’s the same reason areas with a lot of shared or ageing pipework, from Guildford to East Grinstead, generate more repeat callouts than newer builds. If you manage several flats or a shared building, worth checking our coverage for Bloomsbury too.

The Real Cost-Saving Takeaway

The householder in Reigate had already spent £15 on the wrong products before we arrived, and lost a fortnight of a slow-draining sink in the meantime. Learning to unblock a sink properly, matched to what’s actually blocking it, is a five-minute skill that saves both the cash and the wait. Most people only need the bicarbonate-and-vinegar step and a U-bend check. It’s the last five percent, the stubborn ones, where a professional with proper rods earns their fee.

If you’ve worked through this guide and your sink is still holding water, don’t keep pouring things down it. Get in touch with our team and we’ll get an engineer to you who’ll know within thirty seconds of opening the trap which of these two problems you’ve actually got.

Written by a time-served drainage engineer at Drain Cleaning Solution, drawing on two decades of kitchen and bathroom callouts across the UK. Published 13 July 2026. Last updated 13 July 2026.

Understanding how to unblock a sink early helps you budget and avoid bigger repair bills later.