How to Unblock a Sink

The fastest way to unblock a sink is a sink plunger over the plughole with the overflow blocked off — it clears the vast majority of kitchen and bathroom sink blockages in a couple of minutes without opening any pipework. If plunging doesn't shift it, the next step is removing the U-bend under the sink to clear whatever's trapped inside, which solves almost everything else.

A sink draining slowly rather than blocking completely almost always means fat, soap scum or hair has narrowed the pipe rather than sealed it shut, and it's building up gradually every time you use the tap. Kitchen sinks slow down from cooking fat and food particles; bathroom sinks slow down from soap, toothpaste and hair collecting in the U-bend just below the plughole.

Left alone, a slow-draining sink almost always becomes a fully blocked one within a few weeks, so it's worth clearing as soon as you notice it rather than waiting.

Kitchen sinks block from cooking fat, oil and food scraps that set hard as they cool inside the pipe, while bathroom sinks block from hair, soap and toothpaste residue building up in the U-bend. Both types of blockage sit close to the plughole rather than deep in the drain run, which is why most sinks can be cleared without calling anyone out.

Work through these steps in order — most blockages clear at step 2 or step 3, and very few need to go as far as step 5.

1. Bail out any standing water with a cup or jug so you can see the plughole, then remove the plug or basket strainer and check for an obvious clump of hair or food sitting right at the top.
2. Block the overflow hole with a wet cloth, add a little water to the bowl, and plunge firmly 10-15 times without breaking the seal on the plughole.
3. Put a bucket under the sink, unscrew the two slip nuts on the U-bend by hand or with pliers, slide the trap off and clear out whatever's trapped inside before rinsing it under a tap.
4. Refit the U-bend, hand-tighten both slip nuts until snug, and run the hot tap for a minute to check the joints aren't leaking and the water is draining away freely.
5. If it's still slow, feed a hand-cranked drain snake into the waste pipe past the trap, winding it forward until you feel resistance, then twist and pull back to draw the blockage out.

If the sink drains fine on its own but backs up when another fixture is used, or the U-bend was clear when you checked it, the blockage is further down the shared drain run rather than in the sink itself. That needs a drain rod or a plumber's drain snake fed further into the pipe, or in stubborn cases a CCTV drain survey to see exactly where the blockage sits before clearing it.

For blockages affecting more than one sink, a toilet, or an outside drain, see our blocked drains service.

A leaking waste pipe under a sink is almost always a loose slip nut, a perished rubber washer, or a U-bend that wasn't reseated correctly after being cleaned out — and it's usually fixable by hand. Turn off the tap, dry the pipework, hand-tighten each slip nut in turn, then run the tap again and check every joint for drips before putting anything back in the cupboard.

If the pipe itself is cracked, the leak comes from a fixed joint rather than a slip nut, or tightening doesn't stop the drip, that's a job for a plumber rather than more tightening — a cracked waste pipe under a sink can quietly damage a kitchen cabinet or the ceiling below a bathroom for weeks before it's noticed.

Call a plumber if plunging and a U-bend clean-out haven't worked, if more than one sink, the toilet or an outside drain are affected at the same time, or if you can see a cracked pipe or a leak you can't stop by hand-tightening. Those symptoms usually point to a blockage or a fault further down the shared drain run than a plunger or drain snake can reach.

RenoPlumb covers blocked sinks and blocked drains across London and East London, including Tower Hamlets, Hackney, Islington, Newham, Southwark and Canary Wharf, from our base on Commercial Road, E1. See our blocked drains service for what's included, or call 07460 824073 for a free quote.

The cost of unblocking a sink depends on whether the blockage is a simple U-bend clean out or further down the drain run, and whether it's affecting just one fixture or several. We give free, no-obligation quotes for most jobs before starting any work, so there's nothing to lose by asking. See our pricing page for more detail on how jobs are priced.

Need this fixed by someone local? See our page for a plumber in Tower Hamlets for borough-specific coverage and response times.