110mm Soil Pipe: The Complete Guide to Above-Ground Drainage Fittings

110mm soil pipe is the black or grey pipe that carries waste from toilets, and the soil and vent stack on multi-storey buildings and extensions. It is a separate system from plastic waste pipe — different pipe diameter, different fitting types, different rules. This guide covers the Aquaflow 110mm range at APM: when to use solvent weld vs push-fit, the full fitting catalogue, and the venting requirements that catch out builders on first-fix inspections.

110mm Soil Pipe vs Waste Pipe: Know the Difference

Plastic drainage in buildings runs at two scales. 32mm, 40mm, and 50mm waste pipe carries the output from basins, baths, showers, and sinks — small-bore waste. 110mm soil pipe carries toilet waste, the soil stack, and rainwater downpipes on some systems. The two systems connect at a manifold or branch, but they are never interchangeable.

• 110mm soil pipe can carry waste pipe discharge (via a boss adaptor) but not the reverse
• 110mm fittings are not compatible with 50mm waste fittings despite surface similarity
• Soil pipe is always vented to atmosphere — either open to the roof or via an air admittance valve

Black vs Grey: When Colour Matters

The Aquaflow 110mm range comes in black and grey. Both are the same pipe and pressure rating — the colour difference is for installation context:

• Black — conventional above-ground soil pipe, internal and external. The standard colour for new residential work.
• Grey — used when the pipe will be visible in a finished space (utility rooms, exposed pipework) and a less industrial appearance is preferred. Also common in commercial fit-out.

Push-fit fittings (for internal, accessible runs) are available in both colours. Solvent weld fittings are grey (the standard for permanent external and underground connections above the drain).

Push-Fit vs Solvent Weld: Which to Use

The same principle applies here as with waste pipe:

• Push-fit — for internal runs where the pipe may need to be dismantled for maintenance. The rubber seal grips the pipe and allows slight movement. Suitable for vertical stacks inside a building, branch connections at WC, and any run where the joints will remain accessible.
• Solvent weld — for permanent external connections, underground above-drain runs, and any joint that will be concealed in a wall or floor chase. Not demountable once set. Use solvent cement rated for ABS/PVC soil pipe — not the same as 32/40/50mm waste pipe solvent cement.

The Aquaflow 110mm Range at APM

Pipe

• Aquaflow 110mm × 3m Plain End Soil Pipe, Black — £19.11 — plain end for solvent jointing or socketing with a rubber push-fit ring. Three-metre lengths for stacks and external runs.

Couplings

• Aquaflow 110mm Push-Fit Straight Coupling, Black — £4.49 — double socket push-fit for joining two plain-end pipe lengths. Use on internal accessible runs.
• Aquaflow 110mm Solvent Straight Coupling, Grey — £4.09 — solvent weld version for permanent external connections.

Bends

Soil pipe bends come in two angles. Use the correct angle — a 90° tight bend on a WC connection creates blockage risk. The swept 92.5° bend is the standard for WC branch connections because it maintains flow velocity.

• Aquaflow 110mm Solvent Double Socket Swept Bend 92.5°, Black — £5.97 — the standard WC outlet connection bend. The swept radius reduces blockage risk versus a tight 90°.
• 110mm 90° Double Socket Knuckle Bend, Grey — £5.86 — tight 90° for space-constrained direction changes where a swept bend won't fit. Not for WC connections.
• Aquaflow 110mm Solvent 45° Double Socket Bend, Black — £4.90 — for gentle direction changes on long horizontal runs, and for connecting the bottom of a vertical stack to an underground drain at a shallow angle. A 45° bend here reduces impact loading compared to a 90°.

Branches

• Aquaflow 110mm Solvent 92° Triple Socket Branch, Grey — £10.03 — three-way junction for combining two waste inputs and the main stack. Used where a basin waste and bath waste both enter the stack at the same level, or where two WC outlets are close together on a stack.

Boss Connections

Small-bore waste pipe (32/40/50mm) enters the 110mm stack via a boss. There are two methods:

• Aquaflow 110mm Push-Fit Bossed Pipe Connector, Black — £6.44 — a short section of 110mm pipe with a pre-formed boss socket on the side. Replace a plain section with this to create a waste entry point. Available for 32mm, 40mm, and 50mm waste pipe.
• Aquaflow 110mm Strap-On Boss, Black — £2.85 — fits onto an existing 110mm pipe run without cutting out a section. Core drill the pipe, fit the strap-on boss, and connect the waste pipe. Suitable for retrofit connections where cutting the stack is disruptive.

Access and Plugs

• Aquaflow 110mm Access Plug with Screw Cap, Grey — £5.91 — for rodding access on long horizontal runs or at changes of direction. Building Regulations Part H recommends rodding points at 45° bends and every 12m on horizontal runs.
• Aquaflow 110mm Push-Fit Socket Plug, Black — £5.89 — for temporarily capping a stack during installation, or permanently capping an unused branch socket.

Venting: The Regulation Everyone Gets Wrong

Every soil stack must be vented. Without venting, the pressure differential as waste falls down the stack siphons the water seal from traps — you get sewer gas entering the building through dry traps. There are two options:

Open Vent Pipe (Traditional)

The stack exits through the roof with an open-ended vent pipe. Requires a roof penetration, a flashing collar, and the vent must terminate at least 900mm above any openable window within 3 metres horizontally. Simple, permanent, no moving parts.

Air Admittance Valve (AAV)

The AAV (sometimes called a Durgo valve) replaces the open vent pipe. It is a one-way mechanical valve fitted to the top of the stack inside the building — typically in the loft or a cupboard. It opens under negative pressure (when waste falls and creates suction) to admit air, preventing trap siphonage. It stays closed otherwise, preventing sewer gas escape.

• 110mm Air Admittance Valve, Grey (Flopla) — £28.27

AAV restrictions under Building Regulations Part H: the stack must still have at least one open vent at roof level if there are more than five WC connections on the system. On a typical single-house stack (1–3 WCs), an AAV at the top of the internal stack is compliant. Always check with Building Control on extensions — some inspectors require an open vent regardless.

Quick Reference: Fitting Selection by Application

All fittings are available for same-day collection from our Acton trade counter. For extension projects with a complete soil stack list, call ahead and we'll have the full order ready.

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