A drain trap, often called a gully trap, is an external fitting installed in the ground that receives discharge from kitchen wastes, basins, washing machines and downpipes before passing flows into the underground drain. It contains a built-in water seal that blocks foul air rising from the sewer. UK Building Regulations Part H1 specifies trapped gullies for surface and waste connections so that the wider drain system remains sealed against odour. Most gullies have a grating to catch leaves and debris and a removable trap insert for cleaning. Older London properties often have stoneware or cast iron gully traps that can crack over time, allowing root ingress and infiltration. Regular cleaning of the gully grating reduces the risk of overflow during heavy rainfall.
Drain trap (gully trap)
External fitting with a built-in water seal where waste pipes discharge to the drain.
