Hair bound together with soap residue, sitting in the trap or just above it. In a bathroom basin it is almost never anything else, and it is almost never further than 30 cm from the plughole.
Why the trap is the place to look
The trap is the low point, it is where the flow slows, and it is where a hair mass catches on the waste fitting above it. Unscrewing it takes a bucket, two minutes and usually no tools — most bottle traps hand-tighten.
Why chemical openers are a poor first move
They are caustic or acidic, they need contact time, and when they fail to clear the blockage they stay in the trap. Whoever opens it afterwards meets them. They also attack some plastics and coated finishes. If one is used, the product’s own safety instructions govern, and nothing here replaces them.
The mechanical answers, in order of size
A plastic hair grabber — a thin barbed strip, a euro or two — clears a basin from the top. A spring auger of 3 to 5 m reaches past the trap into the branch. Beyond that it is drain work rather than bathroom work.
The preventive one
A hair catcher over the plughole, which turns a yearly job into a weekly wipe.
Questions people actually ask
Is it worth buying a drain auger for a basin?
A 3 m hand auger is cheap and reaches everything a basin can hide. The longer drum types are for toilets and branch runs, and they are the wrong tool for a basin trap you can simply unscrew.
Will boiling water clear it?
It can soften soap and shift a partial blockage, and it must not be poured into a plastic trap or onto a ceramic basin that is cold — thermal shock is a real risk. Warm water and a mechanical tool is the safer combination.
Last reviewed 5 September 2026