Use this guide when water drains slowly, gurgles or will not go down at all in a sink, bath, shower or outside drain. Have rubber gloves, a bucket, old towels, a plunger and a torch ready, and keep children and pets away from the area.
Step by step
Work out how far the problem goes
Check whether only one sink is affected or several fittings are slow at once. A single slow sink usually means a local blockage in the trap or waste pipe. If toilets, sinks and outside drains are all backing up, the blockage is further down the drain and may need professional help.
Remove visible debris
Put on gloves, remove the plug or strainer and pull out hair, food or soap build-up you can reach. Run hot, not boiling, water for a minute to see if flow improves. Avoid pouring boiling water into plastic pipes or toilets, as it can damage joints and porcelain.
Use a plunger properly
Block the overflow hole with a damp cloth so the pressure goes down the pipe. Leave a few centimetres of water in the sink to cover the plunger cup, then pump firmly ten to fifteen times and pull away sharply. Repeat several times before moving on.
Clean the trap under the sink
Place a bucket under the U-shaped trap and unscrew it by hand, keeping any washers safe. Empty and rinse it, clear the pipe ends, then refit it firmly and run water to check for leaks. Tighten by hand only, as overtightening can crack plastic fittings.
Check an outside gully
Lift the grate on the outside gully and scoop out leaves, grease and silt with a gloved hand or small trowel into a bag. Flush with a bucket of water to check it flows away. Never enter a manhole or inspection chamber yourself.
Know when to call for help
If the blockage returns, affects several fittings or sewage is coming up, stop and get help. Blockages in shared or public sewers are usually the water company's responsibility, so contact them first; for private drains, use a reputable drainage firm. Tenants should report the problem to the landlord in writing.
Ready-to-use checklist
- Rubber gloves on
- Bucket and towels in place
- Plug and strainer cleared
- Overflow blocked before plunging
- Trap removed, cleaned and refitted
- No leaks after refitting
- Outside gully cleared
- Water company or landlord contacted if needed
Practical tips
- Never pour cooking fat or oil down the sink; let it cool and put it in the bin.
- Fit an inexpensive hair catcher in showers and baths to stop the most common blockage.
- Avoid mixing different chemical drain cleaners, as they can react and give off harmful fumes.
Common problems
I used a chemical cleaner and the sink is still full of water.
Do not plunge or open the trap straight away, as the chemical may splash onto skin or eyes. Wear gloves and eye protection, follow the product label, and ventilate the room. If you are unsure, call a professional and tell them which product you used.
Water drains but the sink smells bad.
Clean the trap and the overflow, where slime often builds up. Flush with hot water and a little washing-up liquid. If the smell persists or comes from several drains, ask a plumber to check the venting.
The toilet and outside drain are overflowing at the same time.
Stop using water in the house and keep people away from any sewage. Contact your water company, as shared sewer blockages are often their responsibility. Wash hands thoroughly and disinfect any affected hard surfaces afterwards.