Pressurised sewers, or pressure sewers differ form conventional gravity collection systems, because they break down large solids in a grinder pumping station before they are transported through the collection system. The pressure sewer system consist of a series of centrifugal grinder pumps moving finely ground effluent and material along a network of sewers (generally small-diameter). The primary effluent is delivered to the dwelling tank by traditional gravity drainage methods before being ground. Their watertight design and the absence of manholes eliminate extraneous flows into the system. Thus, the systems are an effective solution where conventional systems are impractical such as rocky, hilly and/or water-charged terrain. Moreover, this system requires only shallow trenches and relatively small-diameter piping. Thus, it is also adapted to areas with housing density and where the terrain does not allow gravity flow.