Back-inlet gully

A back-inlet gully has one or more side inlets below the grating that allow waste pipes from kitchen sinks, washing machines or basins to connect directly into the trap chamber. This arrangement avoids the splashing and odour problems associated with discharging over an open grating. Back-inlet gullies are widely used at the rear of UK domestic properties to collect both foul waste and surface water in one fitting before the flow continues to the underground drain. Specifications follow BS EN 1253 for gully gratings and outlets. Modern PVC-U versions feature multiple inlets at different angles, making them flexible to install during refurbishment of older London terraces. Inlets that are not in use must be plugged to maintain the integrity of the water seal.