Abstract: A waste pipe system of an injection moulded or extruded pipe part of thermoplastic material with soundproofing properties having a weight per unit area of at least 8 kg/m.sup.2. The weight per unit area is adjusted by incorporating a filler in the plastic, preferably barium sulphate is used as such a filler. The density of the plastic pipe part is comprised between 1.8 and 2.7, preferably between 1.8 and 2.0 g/cm.sup.3.Suitable thermoplastic materials are PVC, polyolefins and ABS (acrylonitrile-butadiene-styrene) copolymer, particularly PVC or polypropylene.The plastic pipe part may also be a socket or a double sided socket.

Abstract: Method for connecting thin-walled plastic tubes by heat welding wherein a normal plastic tube is heated and provided with a funnel-shaped widening and another tube is heated and provided with a conical narrowing, the narrowing being pushed into the funnel-shaped widening so that these parts are heatsealed to each other.

Abstract: Thermoplastic tube part provided with a polyurethan foam layer with closed skin and containing an inorganic filler for reducing sound production during flow of water through such tube parts.

Abstract: A plastic pipe of a thermoplastic material, such as polyvinylchloride provided on its outside with a resilient sealing body of a polyurethane foam plastic, which has been foamed onto said outside and a layer of thermosetting resin with electrically conducting particles being between said body and the plastic pipe in order to ensure a proper conduction, the foam plastic body having a closed surface being integral with the foam plastic body.