Waste water piping, or tubular mouldings, e.g. pipe fittings suitable for sewerage systems, are extruded, injection moulded or blow-moulded. They are made of polyolefin or polystyrene, incorporating an additive to reach a density of 1.4 - 2.7 g/cm<3>. The tubes or tubular mouldings have an original combination of properties, i.e. the wall thickness is 1/32 of the outer diameter at most, and the length per metre does not exceed 3 kg.