40mm Waste Pipe Fittings — Bends, Branches, Couplings and Knuckle Bends for UK Plumbers

40mm Waste Pipe Fittings — Bends, Branches, Couplings and Knuckle Bends for UK Plumbers

40mm waste pipe is the standard for bath and kitchen sink drainage in UK domestic and light commercial installations. Whether you're routing a bath waste across a floor void, adding a branch for a washing machine standpipe, or negotiating an awkward corner under a kitchen unit, you'll use 40mm fittings daily on site. This guide covers the key fittings, when to use each one, and which Aquaflow products to stock.

APM Electricals stocks the full Aquaflow 40mm waste fitting range at our trade counter in Acton. 24 Western Avenue, London W3 7TZ. Open Monday to Saturday — call 020 8702 8080 to check stock before you travel.

40mm or 32mm — Which Waste Pipe Size Do You Need?

The choice between 32mm and 40mm waste pipe comes down to the appliance and the flow rate:

• 32mm — basin waste, bidet waste, small hand-wash basins. Slower flow rate, lower trap capacity.
• 40mm — bath waste, kitchen sink, shower tray (32mm or 40mm depending on flow rate), washing machine standpipes, and dishwasher waste. Standard for anything with a meaningful flow rate.

BS EN 12056 recommends 40mm minimum for kitchen sinks and baths. If in doubt, go larger — an oversized waste pipe doesn't cause problems, but an undersized one backs up and smells.

Solvent Weld vs Push-Fit — Which Joint Type?

Aquaflow waste fittings come in two jointing systems:

• Solvent weld — permanent joint made with solvent cement. Stronger and fully sealed. Best for concealed runs behind plasterboard, under floors, or in boxing where access is limited. Cannot be disassembled once set.
• Push-fit — rubber O-ring seal. Can be disassembled and adjusted after installation. Suited to accessible runs under sinks and baths, or where the pipework may need to be removed for maintenance. Allows a small amount of movement for thermal expansion.

Both systems are widely used in UK domestic drainage. Check which joints your existing pipework uses before ordering — you can adapt between systems with a spigot fitting if needed.

Key 40mm Waste Pipe Fittings

Knuckle Bend 90°

The 90° knuckle bend makes a tight right-angle turn. It's the go-to for routing waste pipe from a trap or trap outlet around a corner where space is tight — under a kitchen sink, through a cabinet side, or between floor joists. The tight radius keeps the fitting compact inside units. Available in black for exposed runs and white for boxed-in kitchen installations.

Aquaflow 40mm Knuckle Bend 90° Black — £0.97 inc. VAT

Branch 92°

The 92° swept branch tees into an existing waste run to add a second appliance. The slight sweep (92° rather than a dead-right-angle) keeps flow velocity and reduces the risk of blockage at the junction. Typical uses: adding a washing machine standpipe into a sink waste run, connecting two basin outlets to a shared waste, or branching a dishwasher into kitchen waste pipework. The branch angle points slightly downward to encourage drainage toward the stack.

Aquaflow 40mm Branch 92° Black — £1.29 inc. VAT

Bend 135°

The 135° bend makes a gentler 45° direction change. Used where you need to sweep a waste run around a corner without the tight radius of a 90° knuckle bend — for example, where the waste exits a trap at an angle and needs to correct toward a stack or gulley. Less restriction than a knuckle bend, so preferred on longer runs or where there's any risk of slow drainage. Also used to fine-tune the routing where two 90° bends would create too tight a trap arm.

Aquaflow 40mm Bend 135° Black — £0.97 inc. VAT

Straight Coupling

The straight coupling joins two lengths of 40mm waste pipe end-to-end. Essential when a single pipe length isn't enough to reach the stack or gulley, or when a damaged section of pipe needs to be cut out and replaced without disturbing the rest of the run. Also useful where pipe needs to pass through a partition wall — cut the pipe each side of the wall and couple the run through. Available in solvent weld and push-fit variants depending on the jointing system you're working with.

Aquaflow 40mm Straight Coupling Black — £0.97 inc. VAT

Pipe Runs and Fall — Getting It Right First Time

Waste pipe runs above ground must be laid to the correct fall to drain reliably without blockages or self-siphoning of traps:

• Minimum fall: 18mm per metre (approximately 1:50) for 40mm waste pipe
• Maximum fall: 90mm per metre (approximately 1:12) — steeper than this and water outpaces solids, leaving debris in the pipe
• Trap arm length: Maximum 3m for a 40mm trap arm without venting. If the run is longer than 3m, you'll need an air admittance valve (AAV) or stub stack vent to prevent siphoning.

BS EN 12056-2 and the Building Regulations Part H govern sanitary drainage in England and Wales. Always size and install to these standards on new work.

Colour Choice — Black, Grey, or White?

Aquaflow 40mm waste fittings are available in three colours:

• Black — popular for exposed runs, under kitchen units, and utility rooms. Looks clean against white walls and complements grey cabinetry.
• Grey — the traditional UK waste pipe colour. Blends with concrete, screed, and neutral surfaces. Easier to match to older existing grey pipework.
• White — used where waste runs are visible in bathrooms or cloakrooms and a clean, minimal look is needed. Also specified by some kitchen fitters.

Colour choice is cosmetic — all three work identically and are hydraulically equivalent. Pick the colour that matches your existing pipework or the customer's preference.

Where to Buy Aquaflow 40mm Waste Fittings in London

APM Electricals carries Aquaflow's full 40mm waste fitting range — bends, branches, couplings, knuckle bends, spigot bends, reducers, pipe clips, and access plugs — in black, grey, and white. Available for same-day trade collection at our Acton counter. We stock fittings individually for small jobs and can supply in quantity for larger contracts.

24 Western Avenue, Acton, London W3 7TZ. Monday–Saturday. Call 020 8702 8080 or browse the full waste pipe and fitting range online.