The short answer
Most blocked drains come from a handful of causes: fat, oil and food in kitchen drains; wipes, sanitary items and excess paper in toilets; hair and soap scum in bathrooms; and outdoors, tree-root ingress, silt or a collapsed pipe. Slow drainage and gurgling usually mean a partial blockage; sewage backing up or multiple slow drains at once usually point to a problem in the main run.
Identifying the likely cause helps you decide whether to try a quick fix or call someone — and helps you describe the problem accurately when you do.
Common causes
- Kitchenfat, oil, food waste
- Toiletwipes, paper, sanitary items
- Bathroomhair, soap scum
- Outsideroots, silt, collapse
- Warning signmultiple drains slow at once
Inside vs outside blockages
If one sink or toilet is slow, the blockage is usually local and often clearable yourself. If several fixtures are slow, water gurgles, or sewage backs up at an external gully, the problem is likely in the shared or main drain run — that needs a professional and possibly a camera.
Warning signs of a serious problem
- Sewage smell or backing up at a gully or manhole.
- Several drains slow at the same time.
- Recurring blockages in the same spot after clearing.
- Sinkholes, damp or cracking near the drain run outside.
Not sure how serious it is?
We'll match you with a vetted, insured drainage engineer who can diagnose the cause — with a CCTV survey if needed — before recommending any work.
Frequently asked questions
How do I know if a blockage is in my drain or the main sewer?
If only one fixture is affected, it's usually local to your pipe. If several are slow or sewage backs up outside, the blockage is likely in the shared or main run, which is often the water company's responsibility.
Can tree roots block a drain?
Yes. Roots seek moisture and can enter pipe joints, gradually narrowing and blocking the drain. This usually needs jetting and a camera survey, and sometimes a repair.
Why does my drain keep blocking?
Recurring blockages in the same place usually mean an underlying issue — fat build-up, root ingress, a dip or a partial collapse — rather than a one-off. A CCTV survey identifies the cause.
Sources & further reading
Figures on this page are typical UK ranges drawn from published cost guides and are intended as guidance, not a quotation.