Plumbing & water
Blocked sink: the order to try things in
Most blocked sinks are fat (kitchen) or hair and soap (bathroom), and both live in the same place: the trap under the plughole. Work through the methods in order, cheapest and gentlest first, and you will rarely need anything from a bottle.
By the Tickover team · Published 11 February 2026 · 4 min read
Why sinks block where they do
Warm fat pours like a liquid and sets like a candle, and the first cool bend it meets is the P-trap or bottle trap under your sink. Bathroom basins run the same story with hair and soap binding into a felt-like plug. The good news: the usual crime scene is hand-reachable, held on by two plastic nuts.
The unblocking order
Soda crystals and hot water first
For a slow kitchen sink: a good handful of soda crystals down the plughole, then a kettleful of hot water. Fat softens and moves on. Repeat once before escalating.
Plunge with the overflow blocked
Push a wet cloth into the overflow slot, run enough water to cover the plunger cup, then short sharp pumps. Without the cloth, your pressure escapes through the overflow.
Open the trap
Bowl underneath, photograph the assembly, then unscrew the trap by hand. Scoop out the sludge, rinse the trap in a bucket (not in the sink you have dismantled), and refit the washers exactly as the photo shows.
Probe beyond the trap
Trap clean but still blocked? The waste pipe run is next. A flexible drain snake reaches further than anything else on the supermarket shelf.
Chemicals, last and reluctantly
A caustic unclogger can finish a partial fat blockage. It must never be poured into standing water, and it never mixes with any other product.
Keep it from coming back
Every kitchen blockage is a culture problem before it is a plumbing problem. Fat belongs in a jar by the hob (then the bin), pans get wiped with kitchen roll before washing up, and a sink strainer catches what the teaspoons miss. Bathrooms want a hair catcher in the plughole and a monthly pull of whatever it caught.
Sink habits that pay
Do
- Wipe greasy pans with kitchen roll before they reach the sink
- Photograph the trap before you dismantle it
- Block the overflow before you plunge
- Flush the waste with hot water after a greasy wash-up
Don’t
- Do not pour fat down the sink and chase it with hot water, it sets further along, out of reach
- Do not pour caustic cleaner into standing water
- Do not mix drain products, ever
- Do not overtighten the trap nuts on refit, hand-tight seals them
When the sink is innocent
If the sink backs up while the washing machine drains, the machine’s standpipe or the spigot it shares with your waste is the suspect, covered in washing machine won’t drain. If more than one plughole is slow, or an outside gully is standing full, the blockage has moved beyond the house: that is outside drain territory, where the 2011 responsibility rules might make it the water company’s bill rather than yours.
If it beats you
Plumber unblocks a sink
Fixed-fee drainage firm
Typical UK ranges, mid-2026, as a guide only. Your home, your area and the job itself all move the number — always compare real quotes.
Not sure what you’re dealing with?
Tell Self-Diagnose which plugholes are slow, gurgling or backing up, and it will place the blockage, tell you whether it is a DIY job, and brief a vetted plumber or drainage firm if not.
A blocked pan needs a different playbook, no plunging a full bowl for a start: see unblocking a toilet safely. For the whole journey from plughole to sewer, the home plumbing guide joins the pipes up.
Quick answers
What is the best way to unblock a kitchen sink?
In order: soda crystals followed by a kettleful of hot water to soften fat, then a plunger with the overflow blocked by a wet cloth, then unscrew and empty the trap with a bowl underneath. Chemical uncloggers come last, never into standing water. Most kitchen blockages give up at the first or third step.
How do I clean the trap under the sink?
Put a bowl underneath, photograph how everything fits, then unscrew the two plastic nuts by hand and lift the trap away. Empty it, rinse it in a bucket, check the rubber washers are seated, and refit hand-tight. If it drips afterwards, a washer is misaligned; redo it rather than forcing the nuts.
Why does my sink smell even though it drains fine?
A film of fat and food builds up in the trap and on the pipe walls, and the overflow channel harbours its own colony. A soda crystals and hot water flush usually resets both. In rarely used rooms the trap’s water seal can also evaporate, letting drain air in; running the tap for thirty seconds refills it.
Why is water coming back up into my sink?
Backflow means the blockage is downstream of the sink: a shared waste pipe, the outside gully, or the drain itself. If a washing machine empties into the same pipework, its discharge will find the blockage first. Check whether other plugholes struggle, then look at the outside drain before dismantling anything indoors.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
Keep reading
Plumbing & water
Outside drain blocked? Whose problem is it?
Since 2011, shared drains and anything past your boundary belong to the water company. How to tell whose blockage it is, and when the fix is free.
4 min read
Plumbing & water
Unblock a toilet without making it worse
The golden rule is no second flush. How to manage the water level, plunge properly, skip the wire-hanger myth, and tell a blocked pan from a blocked drain.
4 min read
Plumbing & waterFull guide
The homeowner’s guide to plumbing (without the panic)
How water moves through your home, the five failures behind most plumber call-outs, and the two-minute preparations that turn floods into mop-ups.
6 min read