Buchan trap

A Buchan Trap is a device made from fireclay located in a domestic sewer pipe to prevent vermin entering the line. The trap uses a water seal to prevent rats and mice climbing any further along the pipe. Waste flows from the house through a U-bend in the trap. This means that there is always water in the pipe preventing anything from the other direction. The device is a large clay U-bend with air-inlets and vents at the top. It is located below the ground level, but can be accessed through the air-inlet and a rodding hole. This hole allows rods to unblock anything located at the bottom of the U-bend.

The Buchan trap will collect solids, sludge and waste that isn't in suspension and, over time, can clog up. The overflow will back up the pipe and exit from the lowest connected appliance (sink, bath, dish washer, washing machine, etc.). This can be a significant problem in multi-level dwellings (e.g. tenements) where those at the lowest level will receive all the waste waters from those above.

They should be check, and cleaned if required, on a regular basis (say annually)