32mm and 40mm Push-Fit Waste Pipe Fittings — Sizing Guide, Bends, Branches, and Solvent Weld Connections for UK Plumbers

Choosing waste fittings starts with the appliance, pipe system and route. This guide explains 32mm and 40mm choices, fall calculations, bends, branches and transitions. The drainage guidance below is for England; check the applicable local requirements elsewhere.

40mm waste pipe fall per metre

There is no single gradient limit for every 40mm installation. England's Approved Document H, 2015 edition, gives different arrangements:

• Sink or bath: Diagram 3 shows an unventilated 40mm branch up to 3m long, with a slope of 18–90mm per metre.
• Washbasin or bidet: Table 2 gives a 40mm option up to 3m, with 18–44mm fall per metre. Its smaller-pipe options have different length and gradient limits.

Read these with the complete table, diagram and installation conditions. Paragraph 1.20 addresses branch ventilation when the limits are exceeded. A longer run needs a suitable design; do not assume adding an air admittance valve alone resolves every layout.

Calculate the height difference

Total fall in millimetres = horizontal run in metres × fall per metre. For a 2m horizontal run, 18mm/m gives 36mm total fall; 25mm/m gives 50mm. These are calculations, not approval of a particular layout.

• 18mm/m is approximately 1:56.
• 25mm/m is 1:40.
• 90mm/m is approximately 1:11.

Do not use 1:40 as a universal maximum, or assume 1:80 is an acceptable minimum for every 40mm branch.

32mm or 40mm: choose for the appliance and run

Polypipe's waste-system guide identifies 32mm as a typical hand-basin size and 40mm for sinks, baths and showers. Nominal size alone does not settle the design: check the trap, appliance instructions, branch length and any shared discharge before choosing fittings.

Push-fit and solvent weld are different systems

Polypipe distinguishes polypropylene push-fit, using an O-ring seal, from ABS or MuPVC solvent-weld systems. Solvent cement does not bond polypropylene push-fit waste. Follow the selected system's jointing instructions.

A nominal 40mm push-fit pipe and a nominal 40mm solvent-weld pipe can have different outside diameters. Polypipe specifies a suitable universal compression fitting to bridge its different waste systems. Check the fitting's stated pipe-size range and material compatibility; a matching nominal size or colour does not establish compatibility.

Use the specified cleaner, cement, insertion allowance, supports and movement provisions for the actual system. Follow the cement manufacturer's curing and testing instructions rather than applying one drying time to every joint.

Bends, branches and reducers: buying checklist

• Bends: note the existing pipe system and the required change of direction. Check the manufacturer's angle convention before ordering a fitting labelled 92° or 135°.
• Branches: identify the incoming and outgoing sizes and the flow direction. A tee does not establish that a shared run has enough capacity.
• Reducers: confirm both socket sizes and joint types. A reducer changes size; it does not automatically adapt push-fit pipe to a solvent-weld socket.
• Traps and access: check the appliance connection, available space, required seal and access for maintenance.

Find waste fittings at APM

Browse multifit waste fittings. Bring the pipe markings, measured outside diameter and a clear photograph of the existing connection to help identify the correct system. Check each product's current collection or delivery options; long pipe lengths may be collection-only.

APM Plumbing & Electrical
24 Western Avenue, Acton, London W3 7TZ
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Guide reviewed 18 October 2026 against the linked official and manufacturer sources. Refer to the full documents and current product instructions for the installation being designed.