Plumbing
How to unblock a drain—and when to call a plumber
A slow-draining sink or a shower tray filling around your feet usually means something needs attention. Some minor blockages are straightforward to clear. Others need more than another bottle of drain cleaner.
First, work out what’s affected
Is it just one sink, or are the bath, basin and toilet struggling too? A problem affecting one fitting may be close to its plughole or trap. Several fittings backing up can indicate a blockage further along the drainage system.
If wastewater is coming up elsewhere, stop using the affected fittings and arrange help. Adding more water won’t improve the situation.
Remove visible debris
Wear gloves and remove accessible food scraps, hair or soap build-up from the plughole or removable strainer. Follow the manufacturer’s instructions when removing shower-trap inserts or waste covers. Don’t force fittings, push debris further down the pipe or poke around with sharp objects.
Try a suitable plunger
For a sink or basin, a cup plunger can help clear a minor blockage. Cover the overflow opening with a damp cloth and, on a double sink, close the other plughole. Use enough water to cover the plunger cup, make a seal over the waste and use controlled up-and-down movements.
Check whether the water drains afterwards. Stop if connections start leaking or a few attempts make no difference. Don’t plunge a fitting containing chemical drain cleaner: it could splash back onto your skin or into your eyes.
What about cleaning the trap?
The trap beneath a sink can collect debris. Some are designed to be removed for cleaning, but access and fittings vary. Only attempt this if you’re confident you can dismantle and reseal it correctly, and no chemical cleaner has been added.
Put a bucket underneath, avoid forcing connections and check carefully for leaks afterwards. If the pipework is brittle, awkward to reach or already leaking, leave it to a plumber.
Skip the boiling water and homemade mixtures
We don’t recommend pouring a kettle of boiling water into a blocked sink. It can damage some fittings and surfaces, and it won’t reliably remove an obstruction. Bicarbonate of soda and vinegar may fizz impressively, but fizzing doesn’t prove the blockage has cleared.
Never mix drain-cleaning products with bleach, vinegar or other cleaners. If you’ve already used a product, tell the person attending exactly what it was.
If the toilet is blocked
Don’t repeatedly flush a toilet when the water level is rising, and don’t pour buckets of water into an already full bowl. A purpose-made toilet plunger may help with a minor blockage, provided no chemical cleaner has been added. If you suspect a toy or another solid object is lodged inside, forcing it further through can make removal harder.
Know when to call
Arrange help if the blockage keeps returning, several fittings are affected, pipework leaks, or sewage is backing up. For a suspected public sewer blockage, contact Welsh Water. Some shared drains and pipes outside your property boundary may belong to them.
Keep it flowing afterwards
Keep food scraps, cooking fats and oils out of the sink. Clear hair from strainers regularly, and only flush pee, poo and toilet paper. Tell SMC which fittings are affected and we’ll help identify the right next step.