These are joined in the same way as plastic waste pipes but are much bigger-about 100mm (4in) in diameter-so they take longer to fit. They also have some different fittings, such as a soil branch for use where the outlet pipe joins the stack, and access fittings with bolted removable plates for inspection. There are also special connectors to link to the WC pan, via a special gasket, and to link to the underground drainage system which is traditionally made of vitrified clay. The accurate moulding of the fittings and the ease of assembly means that you can confidently tackle complete replacement of a soil system.
Cut the pipe clean and square with a hacksaw or other fine-toothed saw. A useful tip to ensure a square cut is to fold a piece of newspaper over the pipe and join the edges beneath it. The paper will then act as a template. Remove all internal and external ‘burr’ or roughness at the end of the pipe, then use a file to chamfer the outside of the pipe end to about 45°.
Not all manufacturers recommend this, but it does provide an extra key for the solvent. Insert the pipe end into the fitting and mark the depth of insertion with a pencil. Using medium grade abrasive paper, or a light file, lightly roughen the end of the pipe, as far as the pencil mark, and also roughen the interior of the socket. Thoroughly clean the roughened surfaces of the socket and the pipe end using a clean rag moistened with a spirit cleaner recommended by the manufacturer of the fittings.
Select the correct solvent cement (PVC pipes need a different solvent cement from ABS ones; once again, buy all the materials needed at the same time from the same supplier). Read the label on the tin and stir only if instructed. Using a clean paintbrush apply the solvent cement to the pipe end and to the manufacturer may make both PP and either PVC or ABS systems. It is worth asking the supplier if there is an instruction leaflet supplied by the maker. There are slight variations in the methods of using each particular make of pipe and fitting.
The manufacturer’s instructions, if available, should be followed to the letter. Buying new pipe Existing waste pipe is likely to be imperial in size – 11/2in internal diameter for a sink or bath and 11Ain internal diameter for a wash basin. Metric sized plastic pipes are normally described – like thin-walled copper tubes – by their external diameter, though at least one well-known manufacturer adds to the confusion by using the internal diameter. Both internal and external diameters may vary slightly – usually by less than one millimetre between makes. This is yet another reason for sticking to one make of pipe for any single project.
The outside diameter of a plastic tube that is the equivalent of a 11Ain imperial sized metal tube is likely to be 36mm and the inside diameter 32mm. The outside diameter of the equivalent of a 11/2in pipe is likely to be 43mm and the inside diameter 39mm. If in doubt, it is usually sufficient to ask the supplier for waste pipe fittings for a basin waste or – as the case may be – a bath or sink waste. Plain-ended plastic pipe is usually supplied in 3m (10ft) lengths, though a supplier will probably cut you off a shorter piece.
Joining solvent-weld types Solvent-weld fittings are neater and less obtrusive than push-fit ones and they offer the facility of pre-fabrication before installation. However, making them does demand a little more skill and care and – unlike push-fit joints – they cannot accommodate the expansion (thermal movement) that takes place as hot wastes run through the pipe. A 4m length of PVC pipe will expand by about 13mm (just over Vfein) when its temperature is raised above 20°C (70°F). For this reason, where a straight length of waste pipe exceeds 1.8m (6ft) in length, expansion couplings must be introduced at 1.8m intervals if other joints are to be solvent welded.
This rarely occurs in domestic design, however, and use of push-fit or solvent-weld is a matter of personal preference. Although the instructions given by the different manufacturers vary slightly, the steps to making solvent-weld joints follow very similar lines. Of course, the first rule is to measure up all your pipe lengths carefully. Remember to allow for the end of the pipe overlapping the joint. When you’ve worked out pipe lengths cutting can start.