Plastic has replaced traditional materials like lead and copper in the manufacture of waste pipes. Waste pipes are the part of the plumbing system that carry waste (foul) waster from appliances such as washbasins, baths and showers, urinals, kitchen sinks, washing machines and dishwashers to the soil pipe system. The soil pipe system then in turn connects to the underground drainage system.
There are three types of plastic used in the manufacture of waste pipes. These are PVC (Polyvinyl Chloride), ABS (Acrylonitrile Butadiene Styrene) and Polypropylene. All three systems are commonly used in domestic waste systems, whilst PVC is the most commonly used material in commercial installations.
Both PVC and ABS waste systems are known as "solvent weld" systems. This means that joints are made by using a chemical substance (solvent cement) that effectively breaks down the plastic pipe and the joint or fitting and welds or fuses the two parts into one. This makes the joint completely permanent, and unable to leak. Polypropylene waste systems are joined using push fit fittings that incorporate a rubber seal. The simplicity of this system makes it a favourite for DIY fans, as provided the pipe is cut square and clean and the pipe is correctly inserted, the system is easy to assemble. It can also be taken apart and re-assembled if some adjustment in the waste pipe installation is required.
All three systems are designed to cope with the rigours of the domestic waste system. PVC has the best resistance to extremes of temperature, acids and other chemicals and hence this is the material that is usually specified for more commercial installations such as hospitals, police stations and launderettes. Installations such as science labs or photographic laboratories often need even stronger grades of specialist plastics due to the waste chemicals involved.
Waste pipes and fittings come in three sizes, 32mm, 40mm and 50mm. These sizes correspond to the old common imperial pipe sizes of inch and a quarter, inch and a half and two inch. Many plumbers still use this terminology when ordering their materials, so it is important that staff have an understanding of both imperial and metric sizes. Pipe manufacture is not standardised, and most manufacturers produce slightly different size variations - 32mm could actually mean anything from 32mm to 36mm in practice. This means that not all systems are interchangeable, so if you are repairing or extending an existing installation you should ideally take a piece of pipe or a fitting to the retailer to check that the new fittings will actually fit. If they don't fit, don't worry - most manufacturers make a multi-fit compression style fitting that enables to you to join different types of material, including other plastics, lead and copper.
As a rule of thumb, 32mm pipes and fittings are used in conjunction with washbasins (including vanity basins) and some urinals. 40mm is used when connecting to baths, showers, kitchen sinks and other kitchen appliances such as washing machines and dishwashers. Some urinals also have 40mm outlets. 50mm pipes are generally used when a number of appliances use the same waste pipe to join to the soil system, for example in a public convenience where a number of urinals are connected in series to a common pipe.
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