Abstract: A diffuser apparatus for use in a sewage installation includes an elongated, one-piece body of substantially tubular outline in vertical section having a top wall, spaced sidewalls and a bottom wall. An end cap provides a closure for closing each end of the body above the region of the bottom wall to provide a flow path for liquid into and out of a chamber within said body. A plurality of ports are located along each sidewall and a nozzle extends either through one end cap of the topwall for connecting the chamber to a source of compressed air. The flow path for liquid allows debris to flush clear of the chamber. The flow path, in the event that the ports become clogged, provides a distinct bubble pattern at the surface of the liquid during aeration.