50mm vs 40mm vs 32mm Waste Pipe: Which Size Do You Need and How to Use It

Plastic waste pipe is one of the most frequently ordered items on the trade counter — and one of the most frequently ordered wrong. Fitting a 40mm pipe where 50mm is required causes slow drainage and blockages. Fitting 50mm where 32mm is correct means unnecessary material cost and pipework that won't connect to the trap. This guide covers the three standard waste pipe sizes, which appliances use each, the difference between solvent weld and push-fit, and the full Aquaflow range in stock at APM.

Which Size for Which Appliance

The short rule: basins are 32mm, baths/showers/kitchen sinks are 40mm, and the main waste branch to the soil stack from a busy bathroom group is 50mm.

Solvent Weld vs Push-Fit — When to Use Each

Aquaflow waste fittings are available in two connection systems:

• Solvent weld: The fitting and pipe are chemically bonded using solvent cement. The joint is permanent and rigid. Use for concealed runs, runs in floor voids, and any installation that will not need to be dismantled. Solvent weld gives a neater finish and is less prone to working loose over time. Requires priming and cementing both surfaces, then a few minutes to cure before the joint is loaded.
• Push-fit: The pipe pushes into the fitting socket against an O-ring seal. Demountable — can be disconnected for access. Use for surface-mounted installations, runs under sinks, and anywhere future access may be needed. Pipe must be cut square and deburred. Push-fit fittings will not work correctly on out-of-round or burred pipe ends.

You can mix systems in a single waste run, but the transition point must be deliberate — use a push-fit coupling at any point where access is needed, and solvent weld the concealed sections. Do not solvent weld joints that will be behind a permanently sealed surface without a removable access point nearby.

Colours — White, Grey, and Black

Aquaflow waste pipe and fittings are available in three colours:

• White — visible installations in bathrooms and kitchens, where the pipework will be on show.
• Grey — the traditional plumber's choice for concealed runs; blends into backgrounds better than white where not fully hidden.
• Black — for matching to 110mm black soil pipe and drainage systems, or for modern industrial/contemporary interiors.

Mix colours within a system only at reducers or adaptors — do not mix solvent weld white fittings with solvent weld grey fittings unless you confirm they are from compatible manufacturers (the solvent chemistry must be compatible).

32mm Waste Pipe — Basin and Bidet

Pipe

• Aquaflow 32mm Waste Plain End Pipe Grey, 3m — £7.82

Straight Couplings

• 32mm Straight Coupling White — £0.89
• 32mm Straight Coupling Grey — £0.89
• 32mm Straight Coupling Black — £0.89

Bends

• 32mm Knuckle Bend 90° White — £0.89
• 32mm Knuckle Bend 90° Grey — £0.89
• 32mm Knuckle Bend 90° Black — £0.89
• 32mm Bend 92° Grey — £0.89
• 32mm Bend 92° White — £0.89
• 32mm Bend 135° White — £0.85
• 32mm Bend 135° Grey — £0.85
• 32mm Bend 135° Black — £0.85
• 32mm Spigot Bend 45° White — £0.90
• 32mm Spigot Bend 45° Grey — £0.90
• 32mm Spigot Bend 45° Black — £0.89
• 32mm Spigot Bend 92° White — £0.90
• 32mm Spigot Bend 92° Grey — £0.91
• 32mm Spigot Bend 92° Black — £0.94

Tees and Branches

• 32mm Tee Branch 92° White — £1.14
• 32mm Tee Branch 92° Grey — £1.14
• 32mm Tee Branch 92° Black — £1.11
• 32mm Branch 135° White — £1.11
• 32mm Branch 135° Grey — £1.11
• 32mm Branch 135° Black — £1.11

Reducers, Access Plugs, Pipe Clips

• 32mm Access Plug with Screw Cap White — £1.27
• 32mm Access Plug with Screw Cap Grey — £1.27
• 32mm Access Plug with Screw Cap Black — £1.27
• 32mm Pipe Clip White — £0.23
• 32mm Pipe Clip Grey — £0.67
• 32mm Pipe Clip Black — £0.27
• 32mm Push-Fit Socket Plug White — £0.75
• 32mm Push-Fit Socket Plug Grey — £0.75
• 32mm Push-Fit Socket Plug Black — £0.75
• 32mm Waste Adaptor Rubber — £2.83 — flexible rubber adaptor for connecting 32mm pipe to non-standard trap outlets or existing pipework of varying diameter.
• 32mm Rubber Lined Pipe Clip — £1.40 — heavy-duty bracket clip for securing 32mm waste pipe to masonry.

40mm Waste Pipe — Bath, Shower, Kitchen Sink

Pipe

• Aquaflow 40mm Plain End Waste Pipe Grey, 3m — £9.62
• Aquaflow 40mm Plain End Waste Pipe White, 3m — £9.62
• Aquaflow 40mm Single Socket Waste Pipe Black, 3m — £8.06
• Aquaflow 40mm Single Socket Waste Pipe White, 3m — £8.06

Bends

• 40mm Knuckle Bend 90° White — £0.97
• 40mm Knuckle Bend 90° Grey — £0.97
• 40mm Bend 92° Grey — £0.97
• 40mm Bend 92° White — £0.97
• 40mm Bend 135° Grey — £0.98
• 40mm Bend 135° White — £0.98
• 40mm Spigot Bend 45° White — £0.97
• 40mm Spigot Bend 45° Grey — £0.97
• 40mm Spigot Bend 92° White — £0.97
• 40mm Spigot Bend 92° Grey — £0.90
• 40mm Spigot Bend 92° Black — £0.93

Straight Couplings

• 40mm Straight Coupling White — £0.97
• 40mm Straight Coupling Grey — £0.97

Branches

• 40mm Branch 135° White — £1.15
• 40mm Branch 135° Grey — £1.15
• 40mm Branch 135° Black — £1.15
• 40mm Branch 92° White — £1.29
• 40mm Branch 92° Grey — £1.29

Reducers, Access Plugs, Pipe Clips

• 40mm × 32mm Solvent Waste Reducer White — £0.94
• 40mm × 32mm Solvent Waste Reducer Grey — £0.94
• 40mm × 32mm Solvent Waste Reducer Black — £0.94
• 40mm × 32mm Compression Waste Reducer White — £3.43
• 40mm Access Plug with Screw Cap White — £1.29
• 40mm Access Plug with Screw Cap Grey — £1.29
• 40mm Access Plug with Screw Cap Black — £1.29
• 40mm Pipe Clip White — £0.26
• 40mm Pipe Clip Grey — £0.26
• 40mm Pipe Clip Black — £0.23
• 40mm Push-Fit Clip Grey — £0.42
• 40mm Push-Fit Clip Black — £0.48
• 40mm Waste Adaptor Rubber — £4.57
• 40mm Flexible Waste Adaptor Coupling — £4.08
• 40mm Push-Fit Socket Plug White — £0.75
• 40mm Push-Fit Socket Plug Grey — £0.75
• 40mm Push-Fit Socket Plug Black — £0.75

50mm Waste Pipe — The Professional's Choice for Long Runs and Stack Connections

50mm waste pipe is used where flow rate requirements exceed what 40mm can reliably handle — long horizontal runs, busy bathrooms with multiple appliances, commercial installations, and the main waste branch between a bathroom group and the soil stack. Building Regulations Approved Document H recommends minimum pipe sizes based on discharge unit values; for a bathroom group (bath, basin, and WC) the main branch run is typically 50mm.

Pipe

• Aquaflow 50mm Plain End Waste Pipe White, 3m — £13.77
• Aquaflow 50mm Plain End Waste Pipe Grey, 3m — £13.36

Straight Couplings

• Aquaflow 50mm Straight Coupling White — £1.18
• Aquaflow 50mm Straight Coupling Grey — £1.25

Bends

• 50mm Knuckle Bend 90° White — £1.61
• 50mm Knuckle Bend 90° Grey — £1.61
• 50mm Bend 92° White — £1.59
• 50mm Bend 92° Grey — £1.55
• 50mm Bend 92° Black — £1.55
• 50mm Bend 135° White — £1.45
• 50mm Bend 135° Grey — £1.45
• 50mm Spigot Bend 45° White — £1.55
• 50mm Spigot Bend 45° Grey — £1.55
• 50mm Spigot Bend 45° Black — £1.55
• 50mm Spigot Bend 92° White — £1.61
• 50mm Spigot Bend 92° Grey — £1.61
• 50mm Spigot Bend 92° Black — £1.61
• 50mm Solvent 92° Swept Bend Black — £1.59

Branches

• 50mm Branch 135° White — £2.19
• 50mm Branch 135° Grey — £2.19
• 50mm Branch 135° Black — £2.27
• 50mm Branch 135° Grey (heavy) — £2.37
• 50mm Branch 92° Tee White — £2.37
• 50mm Branch 92° Tee Black — £2.37

Access Plugs and Reducers

• 50mm Access Plug with Screw Cap White — £1.43
• 50mm Access Plug with Screw Cap Grey — £1.43
• 50mm × 32mm Solvent Waste Reducer White — £0.89
• 50mm × 32mm Solvent Waste Reducer Grey — £0.89
• 50mm × 32mm Solvent Waste Reducer Black — £0.94
• 50mm × 40mm Solvent Waste Reducer White — £0.89
• 50mm × 40mm Solvent Waste Reducer Black — £0.94
• 50mm Waste Adaptor Rubber — £3.50
• 50mm Pipe Clip Black — £0.37
• 50mm Rubber Lined Pipe Clip — £1.60

Installation Notes

Falls on horizontal waste runs

Waste pipe must run with adequate fall — typically 18–90mm per metre (roughly 1:60 to 1:12). Too shallow and waste sits in the pipe; too steep and the water runs away faster than the solids, leaving blockages. BS EN 12056-2 gives 1:40 (25mm/m) as the recommended fall for 40mm and 50mm waste, and 1:48 for 32mm. For short runs (under 3m from trap to stack), the fall can be steeper without significant risk.

Maximum run lengths before venting is required

Without a vent, waste runs must stay within maximum unvented lengths to prevent trap siphonage. Approved Document H guidelines: 32mm max 1.7m, 40mm max 3m, 50mm max 4m. Beyond these lengths, the pipe must connect to a ventilated branch or use an air admittance valve (AAV) at the trap.

Pipe clipping

Clip waste pipe at 500mm centres on horizontal runs, 1200mm on vertical. Use the correct clip size — an oversized clip allows vibration that can work push-fit joints loose. Rubber-lined clips on masonry prevent vibration transmission and water hammer noise.

All Aquaflow waste pipe and fittings are stocked at our Acton trade counter — 32mm, 40mm, and 50mm in white, grey, and black, in both solvent weld and push-fit. Same-day collection or local delivery available.

APM Plumbing & Electrical | 24 Western Avenue, Acton, London W3 7TZ | 020 8702 8080 | apmi.uk