Kitchen sink draining slowly or completely blocked

A blocked kitchen sink is almost always caused by a build-up of cooking fat, food particles, and soap residue inside the waste pipe. Hot fat poured down the drain solidifies as it cools and accumulates in the U-bend or further downstream.

Start with a plunger. Block the overflow hole (the small hole near the top of the sink bowl) with a wet cloth to prevent air escaping. Place the plunger cup fully over the drain hole, push down firmly 10–15 times, then pull sharply upward. Repeat several times. This works on partial blockages that are close to the drain.

If plunging fails, clear the U-bend (the curved pipe under the sink). Place a bucket under the U-bend, then unscrew the knurled nuts at each end of the bend section (hand-tight plastic, or use pliers for metal). The U-bend should pull out. Clear any debris, rinse it, and refit.

If the blockage is further downstream (beyond the U-bend), use a drain rod or flexible drain snake — push it along the waste pipe to reach and break up the blockage. Alternatively, pour a kettle of hot (not boiling — plastic fittings) water down the drain, followed by a 500ml drain unblocker gel, leave for 30 minutes, then flush with more hot water.

Prevention: never pour cooking oil, fat, or grease down the kitchen drain. Let it cool, decant into a sealed container, and dispose of in general waste or at a recycling centre. A drain guard over the waste hole catches food particles.

If the blockage is in the shared stack pipe or outside drain, or if you have cleared everything accessible and the sink still drains slowly, the blockage may require rods from the inspection chamber outside — or a drain company with a CCTV camera to locate a more serious fault.