How to Unblock a Sink (Without Calling a Plumber)

First: try boiling water

For kitchen sinks, the blockage is often a build-up of grease and fat that has solidified in the pipe. Boiling water dissolves it. Boil a full kettle and pour it slowly down the drain in three stages, giving it 30 seconds between each pour.

Don’t use boiling water on bathroom sinks if you have plastic (PVC) waste pipes — very hot water can soften the joints. Use hot tap water instead.

If the sink is draining again, add a squirt of washing-up liquid first next time to help break down grease before it sets.

Method 2: Bicarbonate of soda and vinegar

This works well on bathroom sinks where the blockage is more likely hair and soap scum than grease. The fizzing action helps break up the clog.

1. Remove any standing water from the sink
2. Pour half a cup of bicarbonate of soda directly into the drain
3. Follow with half a cup of white vinegar
4. Cover the drain with the plug immediately to direct the fizzing downward
5. Wait 15–20 minutes
6. Flush through with hot water

Repeat once if needed. For slow drains rather than full blockages, this is often all it takes.

Method 3: Plunge it

A sink plunger (flat rubber cup, not the flange type used for toilets) creates pressure that dislodges the blockage. Make sure you’re using the right type — a toilet plunger won’t seal properly on a flat sink.

1. Block the overflow hole (the small hole near the top of the basin) with a damp cloth — this stops air escaping and makes the plunger effective
2. Add enough water to cover the base of the plunger cup
3. Place the plunger over the drain and push down firmly to create a seal
4. Pump up and down vigorously 10–15 times
5. Pull off sharply on the last stroke
6. Run the tap to check if it’s cleared

Repeat two or three times if not cleared on the first go. Plunging works best when there’s a solid blockage rather than a gradual build-up.

Method 4: Clear the U-bend

If none of the above has worked, the blockage is almost certainly in the U-bend (the curved section of pipe under the sink). This is straightforward to clear yourself — no special tools needed beyond an adjustable spanner.

1. Put a bucket directly under the U-bend to catch water
2. The U-bend usually has two slip-joint nuts at either end — unscrew these by hand or with slip-joint pliers
3. Pull the U-bend section away and empty it into the bucket
4. Use an old toothbrush or bottle brush to clear any build-up inside the bend
5. Check the pipe sections either side too
6. Refit the U-bend and tighten the nuts — hand-tight is usually enough, don’t overtighten
7. Run the tap and check for leaks at the joints

This sounds more involved than it is — most U-bends come off with no tools at all on modern plastic waste systems. The whole job takes about 10 minutes.

Preventing blockages

• Kitchen sink: never pour fat or oil down the drain — let it cool and bin it
• Bathroom sink: use a hair catcher over the drain, clear it weekly
• Both: pour a kettle of hot water down the drain once a week to keep grease moving
• Run hot water for 30 seconds after washing dishes to push any residue through

We stock sink plungers, drain unblocker, bicarbonate of soda and all the basics at 248–250 Lavender Hill — everything you need to sort it today.