Blocked Kitchen Sink: Causes and How to Fix It

A blocked kitchen sink is the most common drain call we get, and it nearly always comes down to the same thing: fat and food. The kitchen sink takes more abuse than any other drain in the house, and the gunk builds up where you cannot see it. Here is how to clear it and how to stop it happening again.

Why kitchen sinks block

• Fat, oil and grease. This is the big one. Hot fat goes down as a liquid, then cools and sets like candle wax on the inside of the pipe. Over months it narrows the pipe until water can barely get through.
• Food scraps, especially starchy ones like rice and pasta that swell, and fibrous ones like vegetable peelings.
• Coffee grounds, which clump together and sink.
• Soap and detergent scum binding it all together.

How to clear a blocked kitchen sink

Try these in order:

1. Boiling water. If you have metal pipes, a kettle of boiling water poured in two or three goes can melt a soft grease blockage. Skip this if your waste pipe is PVC, the heat can soften the joints.
2. Plunge it. Block the overflow and the second sink (if it is a double bowl) with a wet cloth, run enough water to cover the plunger cup, and pump firmly. Grease blockages often shift with good suction.
3. Clean the P-trap. Put a bucket under the U-bend below the sink, unscrew it, and clear out the gunk by hand. This is where a lot of blockages sit, and it is a fifteen-minute job.
4. Use a drain snake if the blockage is further along than the trap.

Avoid the caustic supermarket cleaners. They rarely shift a real grease blockage and they can damage pipes, we explain why in our guide on chemical drain cleaners.

The grease problem

The single best thing you can do is keep fat out of the sink. Let oil and pan drippings cool, then scrape them into the bin. Wipe greasy pans with a paper towel before washing. A sink strainer catches food scraps before they go down. Do that and a kitchen sink rarely blocks.

When to call a plumber

If you have cleaned the trap and it is still slow, the grease has built up further down the line where you cannot reach it. That needs a high-pressure jetter to scour the pipe walls clean, a plunger or snake just punches a hole through it and it blocks again within weeks. If you are in Newcastle and the sink is still backing up, give us a call and we will clear it properly.