Installed in every UK home from the late 19th century, these traps now form one of the most likely cause of blocked drains (alongside flushable wipes).

A Buchan Trap; showing direction of flow.
The top connector is normally fitted to a pipe running up to
ground level to allow for venting and clearing of the trap.

The small 4" above-ground pipe marking their location is often covered; buried under the drive, in a hedge or even build over

The elusive Buchan trap;
David Attenborough might struggle to find some of them!

History of the Buchan Trap

Concerned about Cholera infesting houses through sewer vapours, WP Buchan, a Glasgow sanitary engineer patented the Buchan Trap device in 1875.

Despite Dr. John Snow’s research in Soho some 20 years earlier showing cholera wasn’t an airborne contagion, that didn’t immediately kill off the airborne disease theory. Buchan designed his trap on the same principle as the toilet U-bend. By inserting a similar bend in the earthenware pipe that took sewage from the house, he created a water seal that prevented foul air escaping from the street’s main sewer into the house, where it might have laid low the inhabitants of every room. As an additional benefit, it would also stop the ingress of rats. New building regulations insisted that the trap be installed in every house. Some were known as “interceptors” and others as “blind syphons”, and many took the names of their locality; the “Bristol interceptor”.

Today we know rats simply swim past the traps and cholera is contracted only through direct contact with contaminated water. The Buchan trap now only serves to restrict the flow of waste from your home and in creating such a choke point, often does just that! Furthermore, fired clay only has a lifespan of some 50-70 years, after which it will degrade, this leads to cracking and the Buchan trap has many fail points. Only small ground movement can cause total failure. See below, the trap has been removed, leaving the connections in place (each connection had cracked through completely)

If you are experiencing blockages or the toilet / bath are slow to empty, this little trap may well be the problem. SBS can provide a CCTV sewer survey to identify the existence of - and problems with - your Buchan trap, along with other issues such as hidden manholes, failing pipework and presence of pitch fibre.

If you are looking to purchase an older property, a sewer survey is a very good idea. The cost of a survey (around £300) will almost certainly be significantly less than replacing pipework or removing failed traps once you are the owner. Home reports and most property surveys do not physically check sewer lines, and repeat blockages do not have to be reported to prospective purchasers.

A standard repair; Clay to clay repair after removing
a failed buchan trap at the end of the driveway.