Why your drains keep blocking, and what actually helps

Most repeat blockages are not bad luck. Something is either going down the drain that should not, or the drain itself has a fault that keeps catching whatever passes.

What causes it

• Fats and oils. Liquid in the pan, solid in the pipe. They coat the inside of the run and everything else sticks to them.
• Wipes. Including the ones sold as flushable. They do not break down the way paper does.
• Hair and soap. The usual pair in a bath or shower waste, and the reason a slow drain gets slower over months rather than overnight.
• Root ingress. Roots find their way into old clay joints and then hold on to everything that passes.
• A fault in the run. A collapsed section, a displaced joint or a fall that is too shallow. A drain like this will block again whatever you put down it.

What helps

Scrape plates and let fat set before it goes in the bin rather than the sink. Fit a hair trap in the shower and clear it weekly. Only paper down the toilet. If a gully outside keeps filling, keep leaves and silt out of it.

What does not

Chemical unblockers are worth one attempt on a slow sink. On a properly blocked run they mostly sit on top of the blockage, and then someone has to work in a pipe full of caustic liquid. They also do nothing at all about roots or a broken pipe.

When it is worth looking properly

If the same drain blocks more than once in a year, clearing it again is treating the symptom. That is the point at which it is worth finding out what shape the run is actually in.