Why does waste pipe come in different sizes - 32mm and 36mm - 40mm and 43mm?

Good question.

The simple answer is that there are two different types of waste pipe, push fit waste pipe which is measured in metric terms and solvent weld waste pipe which is often measured in imperial terms. To the layman eye they look like the same size and to make matters less clear both push fit and solvent weld are advertised in metric terms, 32mm, 40mm or 50mm as both types have this as an internal diameter.

Compression fittings can be used on either solvent weld or push fit pipe, however are more bulky and expensive. A size chart is shown below and sometimes the type of pipe you have is printed o the side of the pipe (if you see ABS printed this is solvent pipe)

Advertised Dimension Push Fit Diameter Solvent Weld Diameter Compression compatible
21.5mm N/A 21.5mm Not available except on
some condensate traps
32mm 34mm 36mm (1 1/4") Yes - all
40mm 41mm 43mm (1 1/2") Yes - all
50mm 54mm 56mm (2") Yes - all
110mm 110mm 110mm Not available

As the name suggests push fit pipe is connected using push fit fittings which have there own internal seal and do not require any additional sealing. Solvent Weld pipe requires that a solvent weld cement (similar to glue) is used on the joint which literally welds the two together, forming a very strong permanent seal.

Solvent Fittings and push fit fittings cannot be interchanged i.e. you cant use a solvent fitting on push fit pipe or vica-versa. As well as the obvious size differences (apart from 110mm) they are made of different materials and in particular only solvent weld pipe and fittings will weld using solvent cement.

NB Chrome waste pipes are supplied in 35mm and 42mm sizes, a conversion seal or fitting is required to connect them to plastic pipework

You can see a link to both all types of drainage sections on our website below:

1st Mar 2020 Matt

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