How to unblock a sink: 6 things to try before calling a plumber

In a kitchen, the cause is nearly always cooking grease and food scraps: the fat sets in the trap and pipes, catches debris and eventually forms a blockage. In a bathroom sink, it's mostly hair and soap and toothpaste residue clinging to the plug.

The early signs: water drains slowly, gurgling, then bad smells coming up from the plughole. At that stage a simple fix often works. Once the water stops draining altogether, you need to get to the blockage itself.

This is the first thing to try on a kitchen sink that drains slowly. Scoop out standing water with a glass, squeeze a good dose of washing-up liquid into the plughole, then pour in a litre of very hot water. Leave it a few minutes, then run the hot tap to rinse.

The washing-up liquid breaks down grease and the hot water carries it away. It helps with greasy build-up, not with an object stuck in the pipe.

Careful with boiling water. If your waste pipes are plastic (grey or white pipes under the sink), don't use boiling water: it can warp the pipes and seals. Very hot tap water, or a kettle switched off just before it boils, is enough.

The best-known home remedy works on a slow drain or bad smells, much less on a real blockage.

1. Empty the sink — Scoop out standing water so the mixture reaches the blockage.
2. Pour in the bicarbonate — Pour half a cup of bicarbonate of soda (baking soda) straight into the plughole.
3. Add the vinegar — Pour in a cup of white vinegar, then cover the plughole with a cloth: the mixture fizzes and works inside the pipe.
4. Leave it 30 minutes — Then flush with very hot water. Repeat once if it drains better but not yet normally.

What about soda crystals?

Soda crystals (washing soda, not to be confused with caustic soda) cut through grease well: two tablespoons in a litre of hot water, poured down the plughole, then rinse. Wear gloves, as they irritate skin and eyes, and never mix them with another product.

A plunger is still the most effective tool for unblocking a sink or basin. Leave a little water in the sink to cover the plunger cup. Block the overflow (or the second bowl of a double sink) with a damp cloth: otherwise the pressure escapes. Pump firmly about ten times, then pull away sharply.

Repeat two or three times. If the water starts going down, run hot water to flush away what's left.

The trap is the U-shaped or pot-shaped part under the sink. That's where grease, food debris and hair build up. Anyone can take it off, and it fixes a large share of blocked sinks.

1. Get ready — Empty the cupboard under the sink, put a bucket and towels under the trap.
2. Unscrew by hand — Plastic nuts come off without tools. Keep the washers safe.
3. Clean it — Empty the trap, scrub off deposits with an old brush and rinse with hot water.
4. Refit and test — Screw back by hand with the washers seated properly, run the water and check for drips.

Trap clean but the water still won't drain? The blockage is further down the pipe. A drain snake (or hand auger) is a simple tool from any DIY shop: a flexible coiled cable with a handle.

With the trap off, feed the snake into the pipe going into the wall, pushing gently while turning the handle. When you feel resistance, keep turning to hook or break up the blockage, then pull the cable out. Refit the trap and flush with hot water.

A hand snake reaches a few metres. If the blockage is in the building's soil stack or under the floor, it's a job for a plumber with an electric drain machine.

A bathroom sink usually blocks because of hair wrapped around the pop-up plug rod. Under the basin, undo the nut holding the rod, lift out the plug, clean it and fish the hair out with a plastic hook.

Then it's the same as a kitchen sink: plunger with the overflow covered, and take off the trap if needed.

• Strong chemical drain cleaners (caustic soda, acid): they damage seals, can attack some pipes and make the job dangerous if they sit in the sink.
• Mixing products: some give off toxic fumes.
• Poking with a coat hanger or screwdriver: you can pierce the trap or push the blockage further in.
• Boiling water on plastic pipes: it can warp them.
• Keeping the tap running in the hope it clears: the sink will eventually overflow.

In these cases you need a plumber with an electric drain snake. See our blocked sink page, or blocked drain if several outlets are affected. Send us a photo on WhatsApp: we'll tell you if a simple fix will do, otherwise we give you the price before we come.

• The trap is clean, the drain snake didn't help, and the water still won't drain.
• Several drains are blocked at once, or water comes up in the shower when you empty the sink.
• The blockage comes back after a few days.
• A persistent bad smell, or gurgling in other rooms.
• A chemical product has already been poured in and is sitting in the sink.

For every other water problem, see our plumber in Luxembourg page.

• Never pour cooking fat down the sink: let it set, then bin it.
• Wipe plates and pans with kitchen paper before washing.
• Use a strainer on the kitchen plughole and a hair catcher on the bathroom basin.
• Coffee grounds go in the bin or compost, not the sink.
• Once a week, pour a litre of very hot water with a little washing-up liquid down the drain.