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

Above-ground waste drainage in UK properties runs on two pipe sizes: 32mm for hand basin waste and 40mm for bath, shower, and kitchen sink waste. Getting the size right, choosing the correct joint type, and selecting the right fittings for the run are the decisions plumbers make on every domestic job. This guide covers push-fit and solvent weld 32mm and 40mm waste fittings, when to use each, and how to build a reliable above-ground drainage run to Part H of the Building Regulations.

32mm vs 40mm Waste Pipe: When to Use Each

UK above-ground drainage follows BS EN 12056-2, which specifies pipe sizing based on discharge unit values. In practice, the rule is straightforward:

• 32mm waste pipe — hand basins (WHBs), bidets. Low flow rate, short horizontal runs to a soil stack or hopper.
• 40mm waste pipe — baths, showers, kitchen sinks. Higher flow rate and longer permissible runs.

Maximum fall for both is 1:40 (25mm per metre). Minimum fall is 1:110 (9mm per metre) for 32mm and 1:80 (12.5mm per metre) for 40mm. Steeper falls cause siphonage of the trap seal; shallower falls cause blockage. If you are running a 40mm waste more than 3m to the stack without an air admittance valve (AAV), you are at risk of trap seal loss — fit a resealing trap or an in-line AAV.

Push-Fit vs Solvent Weld Waste Fittings

Both systems are in widespread use for above-ground plastic waste. The choice affects installation speed, future access, and thermal expansion management.

Push-Fit Waste Fittings

Push-fit fittings use rubber O-ring seals. They allow thermal expansion movement, which matters on long kitchen sink runs where hot water causes measurable pipe expansion. Key advantages:

• Quick to install — no priming or cement, no cure time
• Demountable — fittings can be disassembled for clearing blockages or future alterations
• Accommodates movement — the pipe can slide in the socket during thermal cycling

Disadvantage: the rubber seal can perish over decades in aggressive environments, and push-fit joints can pull apart if not retained on long horizontal runs. Use pipe clips at least every 500mm on horizontal 40mm waste, 300mm on 32mm.

Solvent Weld Waste Fittings

Solvent weld (SWC) fittings are chemically bonded using solvent cement. The joint is permanent, rigid, and compact — useful where space is tight, such as inside a vanity unit. Key points:

• Prime all surfaces with Tangit or equivalent cleaner before applying cement
• Joint cure time: 5 minutes before stress, 24 hours before water test
• No thermal movement allowed — allow expansion loops on long runs
• Grey is the standard colour; white and black available for concealed/aesthetic applications

Core 40mm Waste Fittings

40mm Branch 92° Grey

The 92° branch fitting (sometimes called a swept tee) connects a branch waste pipe into the main run at 90°. Used where a basin or bidet discharges into a combined 40mm waste serving a bath or shower on the same horizontal run. The swept entry reduces turbulence and minimises blockage risk. Available push-fit or solvent weld — match the system you are installing.

40mm Solvent Weld Bend 135° Grey

The 135° bend (45° change of direction) is the standard fitting for redirecting a waste pipe at shallow angles — routing around a structural element or making the turn from a vertical drop to a horizontal run. Solvent weld gives a rigid, compact connection ideal for under-sink spaces and inside cabinet runs.

Core 32mm Waste Fittings

32mm Tee Branch 92° Grey

The 32mm tee branch is the standard fitting where two basin wastes need to combine on a shared run — twin hand basins in a cloakroom, for example. It can also accept the waste from a second basin into a floor-routed 32mm run before it rises to discharge into a hopper or 110mm soil stack via an adapter. The 92° swept entry is preferred over a straight tee to keep flow velocity consistent and reduce settlement.

Reducing Between 40mm and 32mm

40mm × 32mm Reducer

Where a 32mm basin waste discharges into a 40mm combined run — the most common scenario in bathroom layouts with separate basin and bath wastes sharing a single exit point — the 40mm × 32mm reducer makes the transition. It is also used where 32mm solvent weld pipe enters a 40mm push-fit manifold.

Waste Pipe Sizing and Material: Practical Notes

MUPVC vs ABS

Most plastic waste fittings are MUPVC (modified unplasticised PVC), which is compatible across brands for push-fit and solvent weld systems. ABS fittings are also available and more common in commercial applications. Do not mix solvent cements — use the correct cement for the material. Tangit PVC-U works on MUPVC; ABS requires ABS solvent cement. Push-fit systems are cross-compatible provided pipe OD is consistent.

Pipe Clips and Support

Unsupported waste pipe will sag, reducing fall, and eventually cause blockages. BS EN 12056-2 recommends:

• 32mm: pipe clips every 300mm on horizontal runs
• 40mm: pipe clips every 500mm on horizontal runs
• Both: at least one clip within 150mm of each fitting

Use saddle clips screwed to joists or noggins. On masonry, plastic pipe clips with wall plugs. Avoid over-tightening on push-fit systems — the pipe must be free to expand longitudinally.

Trap Selection for 32mm and 40mm Waste

Every waste outlet requires a trap maintaining a 75mm water seal (BS EN 274). For 32mm basins, a 32mm bottle trap or P-trap is standard. For 40mm bath and shower waste, a low-profile shower trap (flat trap) or bath P-trap is used. Kitchen sinks typically use a 40mm P-trap or bottle trap depending on the waste configuration. Where back-pressure is a risk (e.g., ground-floor waste into a full soil stack), use a resealing trap.

Connecting to the Soil Stack

Above-ground 32mm and 40mm waste pipes ultimately discharge to either:

• 110mm soil and vent pipe (SVP) — via a 110mm strap boss (for 40mm) or 110mm reducer boss (for 32mm and 40mm). Each soil stack can accept a limited number of discharge units per storey.
• External hopper head — open hopper collecting 32mm/40mm waste from upper floors. Note: open hoppers cause odour escape and are now discouraged by BS EN 12056. Acceptable only where already existing on older properties.
• Ground-floor direct connection — short-run discharge to a trapped gully. Maximum 3m run for 40mm, 1.5m for 32mm without additional ventilation.

Part H Building Regulations: What You Need to Know

Approved Document H (2002, amended 2010) covers above-ground drainage. Key requirements for 32mm and 40mm waste:

• All waste connections to discharge into a trapped gully or soil stack — no direct connection to a rainwater system
• Trap seal minimum 75mm on all sanitary appliances
• Ventilation required on long runs exceeding the branch pipe length limits (3m for 40mm, 1.7m for 32mm without ventilation)
• Air admittance valves (AAVs) permitted where a stack vent is not practicable — must comply with BS EN 12380
• Testing: water test or air test to 38mm water gauge for 5 minutes on completion

Summary: Choosing the Right Waste Fitting

For fittings that connect to 110mm above-ground soil pipe, see our 110mm Soil Pipe and Waste Fittings guide. For bathroom electrical accessories that accompany drainage installations, see Bathroom Electrical Accessories. For push-fit plastic pipework systems covering barrier pipe and Speedfit, see Plastic Pipework Systems. For central heating and boiler connections, see Boiler Filling Loops.

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