How to Clean Your Kitchen Pipes (and Stop the Sink Blocking)

The kitchen sink blocks more often than any other drain in the house, and it's nearly always the same culprit: fat.

Cooking oil and fat go down the drain as a warm liquid, hit the cold pipe a metre or two along, and solidify. Over months, that layer builds up like cholesterol in an artery, and every bit of food scrap and coffee ground that follows gets caught in it.

Here's how to clean it out properly, and how to stop it coming back.

Start with hot water and dish soap

For a sink that's draining slowly rather than fully blocked, this fixes it more often than people expect.

Boil the kettle. Squirt a generous amount of dish soap directly into the drain, then pour the boiling water down slowly, in two or three goes with a pause between each. The soap emulsifies the fat and the heat keeps it moving.

Repeat it a second time if the water is still draining slowly. If it's a fat build-up in the early stages, this genuinely clears it.

One caution: if you have PVC waste pipes — which most homes built since the 1970s do — use very hot tap water rather than boiling. Repeated boiling water can soften and distort PVC joints.

Then bicarb and vinegar

If hot water alone didn't do it, try this before you reach for anything harsher.

1. Pour half a cup of bicarbonate of soda into the drain.
2. Follow it with a cup of white vinegar.
3. Cover the plughole with a plug or cloth and leave it 15 minutes.
4. Flush with hot water.

The fizzing reaction lifts residue off the pipe wall. It's mild, it's cheap, and unlike caustic cleaners it won't damage your pipes or make the job hazardous for the next person who opens the line up.

Clean the P-trap

The P-trap is the U-bend under the sink. It's designed to hold water so sewer gas can't come back up, and it's also where most solid blockages sit.

1. Put a bucket underneath it — it will be full of water.
2. Unscrew the two slip nuts by hand. They're usually hand-tight; if not, use multi-grips gently.
3. Pull the trap off and tip it out.
4. Clean it through with a bottle brush and hot soapy water.
5. Reassemble, hand-tighten, and run the tap to check for drips.

This is well within most people's ability and it clears a surprising proportion of kitchen blockages outright.

Why we'd rather you skipped the chemical drain cleaner

Caustic drain cleaners are the go-to and they're usually the wrong answer.

• They rarely shift an established fat blockage — they burn a channel through it and the rest stays.
• They damage older pipework, rubber seals and chrome fittings.
• They sit in the trap and make it genuinely dangerous for whoever opens that pipe next, which may well be you.

If a plunger and a P-trap clean haven't fixed it, the blockage is further down the line than any chemical is going to reach.

Stopping it happening again

• Never pour fat or oil down the sink. Let it set in a jar or tin and bin it.
• Wipe greasy pans out with paper towel before washing them.
• Use a sink strainer and empty it into the bin, not the drain.
• Run hot water for ten seconds after washing up.
• Do the bicarb and vinegar flush monthly. Five minutes, and it prevents most kitchen blockages entirely.
• Coffee grounds go in the bin. They clump and they're one of the worst things for a kitchen drain.

When it's beyond a DIY fix

Call a plumber if:

• The sink is completely blocked and a plunger and trap clean haven't worked
• Water backs up into a second fixture when you run the sink — that means the blockage is in the main line
• There's a sewage smell
• It blocks again within a few weeks of being cleared

That last one matters. A drain that keeps re-blocking has an underlying cause that nobody has found — usually tree roots at a pipe joint, a crack, or a section of pipe that has sunk and holds water. A drain camera inspection identifies which in about fifteen minutes, and until you know, you're just paying for the same clear over and over.