Blocked Kitchen Sinks

In short: Kitchen sinks block because fat, oil and food scraps go down warm, then cool and stick to the inside of the waste pipe until it closes up. Cleaning the trap under the sink fixes many blockages. If the water still won't go, the blockage is further along the waste pipe or in the outside gully and needs rodding or jetting.

The kitchen sink takes the hardest waste in the house. Gravy, frying oil, rice, pasta, coffee grounds and the last of the washing-up water all go the same way, and fat in particular sets like candle wax once it cools. Washing-up liquid only moves it a little further down before it sets again.

That's why kitchen sinks usually slow down gradually, and why a quick fix at the plughole often only lasts a few days.

Clean the trap first

Under most sinks there's a U-shaped or bottle trap that unscrews by hand. Put a bowl underneath, unscrew it, empty it and rinse it out. A surprising number of blockages are just a trap packed with food. Check the washers are seated properly when you screw it back, or it'll drip.

If that doesn't work

With the trap clean and water still standing, the blockage is in the waste pipe running through the wall, or in the gully outside where it empties. Look at the gully: if it's full of grey water and grease, that's your blockage. If the gully is clear, it's in the pipe. A sink plunger may move a soft blockage, with the overflow covered by a damp cloth so the pressure goes down the pipe rather than out of it.

Why we don't recommend chemical unblockers

Caustic products can dissolve a little grease, but on a solid blockage they sit in the pipe, often for hours, and leave a hazardous pool for the next person who has to open the trap. They can also soften plastic fittings and corrode old metal ones. Clearing the pipe mechanically is quicker and leaves it properly open.

How we clear kitchen sink blockages

Depending on where it is, we use a hand auger on the waste pipe, rods through the gully, or jetting for a pipe that's lined with grease along its length. Jetting matters here because it removes the coating on the pipe wall, not just the plug in the middle, so the full width of the pipe is clear again.

Keeping a kitchen sink clear

• Wipe greasy pans with kitchen roll and bin it before washing up
• Let cooking oil cool, pour it into a container and bin it
• Use a plughole strainer to catch food scraps
• Keep coffee grounds and rice out of the sink, as they swell and settle in the pipe

For restaurants and takeaways, fat is an ongoing issue that needs grease management and planned maintenance. See commercial drainage.

Questions people ask