How to unblock a kitchen sink: 5 methods from gentle to heavy duty

What you need

• 10 litre bucket and a cloth
• Rubber gloves
• Flat-cup sink plunger (5-9 € at Leroy Merlin or Bricodepot)
• 3 or 5 m hand drain snake with crank handle (Wolfpack or Rothenberger Rospi, 10-25 €)
• Box spanner or adjustable pliers for the trap
• Torch
• Concentrated washing-up liquid (Fairy or similar)
• Bicarbonate of soda and white cleaning vinegar (optional, as an intermediate step)
• Caustic gel drain unblocker (HG, Mr Muscle or Desatascador Forza, 4-9 €) only as a last resort
• New 40 mm bottle trap or set of washers in case the old one is damaged (Jimten or Wirquin, 5-10 €)

Step by step

1. 1

   Method 1: very hot water with washing-up liquid

   Bail the standing water into the bucket with a cup. Squirt a generous amount of washing-up liquid straight into the drain, then pour in two litres of very hot water, not boiling. Wait 10 minutes and check whether it drains. Works on recent fat blockages.

2. 2

   Method 2: plunger with the overflow covered

   Fill the bowl with 5 cm of water. Cover the overflow and the second bowl with a wet cloth. Seat the plunger over the drain and pump 10-15 times hard, pulling up sharply on the last stroke. Repeat three times.

3. 3

   Method 3: take apart and clean the trap

   Put the bucket underneath. Loosen the bottom nut of the bottle trap by hand (or the two nuts on an S trap) and take it off. Empty the fat into the bucket, never down another drain, and wash the trap with hot water and washing-up liquid. Check the washers and refit it hand tight, no tools.

4. 4

   Method 4: hand snake down the wall pipe

   With the trap off, feed the snake into the pipe that goes into the wall. Advance by turning the crank clockwise and pushing gently. When you feel resistance, turn without pushing until it gives, then pull the snake out slowly, wiping it with the cloth. Refit the trap and run the hot tap for 3 minutes.

5. 5

   Method 5: chemicals, only if the above has failed

   With the sink empty of water and no other product used beforehand, pour in the dose on the bottle, leave for the stated time (usually 30 minutes, never overnight in plastic pipes) and rinse with plenty of cold water. Gloves and goggles. If it does not work, do not repeat: call.

6. 6

   Check and prevent

   Fill the bowl and release it in one go: it should drain in under 10 seconds without gurgling. Fit a fine strainer in the basket and repeat the hot water with washing-up liquid once a month.

Before unblocking the kitchen sink: where the clog is (fat, scraps and trap)

A kitchen sink drain has three places where a blockage forms. The first is the waste and strainer basket in the bowl: food scraps that will not fit through the holes. The second is the trap, the bottle or S-shaped part under the sink that holds water to stop smells rising: that is where fat collects, cools and hardens. The third is the wall pipe, 40 or 50 mm, running to the stack: when the blockage is there, the water drains very slowly or not at all.

In 80 % of kitchens the cause is fat. Oil from the frying pan, stock, butter and cream go down as liquids with the hot water, but a metre from the sink the pipe is cold and the fat solidifies on the inside wall. Layer by layer, the 40 mm pipe shrinks to 15. Then a handful of rice, coffee grounds or a piece of onion skin finishes the job. Coffee grounds and rice are the worst: they do not dissolve and pack down with the fat.

To find out where the blockage is, watch how the water behaves. If the sink does not drain at all and the rest of the house works, the blockage is local: strainer, trap or the first metre of pipe. If the dishwasher also will not empty, or water comes up in the sink when the washing machine drains, the blockage is in the shared pipe or the stack, and home methods will not reach it.

Mistakes when unblocking a sink that will not drain at all

The most common mistake is starting with chemicals. A gel unblocker that fails to get through the clog sits in the trap, and when you take it apart or use the plunger, it splashes caustic soda in your eyes and on your hands. It also corrodes old plastic traps and seals. Chemicals are the last step, never the first, and two different products are never mixed.

The second mistake is pouring boiling water straight from the pan into a sink with PVC pipes. At 100 degrees PVC softens and glued joints give way. Use very hot water from the tap, or from the kettle left to stand for two minutes, but not boiling. The third is using the plunger without covering the overflow or, on a double sink, without covering the other bowl: the pressure escapes there and the plunger does nothing.

And one we see every week: taking the trap apart with no bucket underneath and without noting the order of the washers. A bottle trap has two or three conical washers that only seal in one position; fit them the wrong way round and it drips under the unit for weeks and swells it. Take a photo before you loosen anything.

When to call a professional

Call when the water does not drain at all after cleaning the trap, when the blockage comes back within a month, when several drains in the home run slow at the same time, or when the hand snake stops at 2 or 3 metres and will not go further. Those are signs that the fat is in the wall pipe or in the branch to the stack, and that needs the electric snake machine, which scours the fat off the pipe wall instead of just punching a hole through it.

Unblocking a kitchen sink costs 70-120 € including call-out, and 110-180 € if we have to go in with the snake machine; at night or on a public holiday, 130-220 €. If the blockage keeps coming back, we do a camera inspection (60-120 €, free if you book the unblocking) to find the section with fat or a break. Prices are in how much drain unblocking costs and the service in drain unblocking. We arrive in 20-45 minutes in Valencia, Alicante, Torrevieja and Benidorm.

If you are in the city, we have a page with local response times and prices for drain unblocking in Valencia; also for Alicante, Torrevieja and Benidorm.

Hard water and coastal kitchens: why sinks block more often

The water in Valencia and Alicante is hard, with a lot of limescale. Scale builds up inside the pipe and forms a rough surface that fat clings to far better than to smooth PVC. That is why on the coast a sink blocks twice as often as in soft-water areas, even with the same cooking. Add to that the many second homes in Torrevieja or Calpe that sit closed for months: the water in the trap evaporates, the fat dries and hardens, and when you come back in summer the sink will not drain.

Prevention that works: once a month, two litres of very hot water with washing-up liquid, and before you lock up the property, the same plus a spoonful of oil in the trap so the water does not evaporate. Never pour used cooking oil down the sink; in Valencia and Alicante there are orange collection bins in almost every neighbourhood. And a fine strainer basket (1-2 € at the bazaar or Leroy Merlin) for the rice and coffee grounds.

Related guides

If you would rather try a remedy without products first, read unblocking drains with baking soda and vinegar, where we explain when it genuinely works. If the dishwasher will not drain either, see how to unblock a dishwasher. And if none of this works, how to clear a badly blocked pipe.