110mm Soil Pipe Fittings — Pushfit Connectors, Socket Plugs, Bends, and Branches for UK Plumbers

110mm soil pipe is the standard above-ground drainage diameter in UK domestic and commercial properties. It carries WC waste from toilets to the soil stack, connects soil stacks to underground drainage, and forms the main vertical drain run in two-storey homes. Getting the right fittings — socket plugs, bends, branches, and couplings — is essential for a clean, leak-free installation that meets Building Regulations Part H.

This guide covers pushfit 110mm fittings for above-ground systems, the difference between grey and black versions, how to size branches, and when solvent-weld is required instead of pushfit.

Soil Pipe vs Waste Pipe: Know the Difference

110mm pipe is specifically soil pipe — it carries WC (foul) waste containing faecal matter and urine. This distinguishes it from waste pipe (32mm, 40mm, 50mm) which carries sink, basin, bath, and shower waste. The two systems must not be confused:

Soil pipe connects directly to the underground drainage system (100mm vitrified clay or uPVC) via an adaptor at ground level. Never connect 40mm waste pipe directly to a 110mm soil stack without a trap — the pressure differential will siphon traps and allow sewer gas into the property.

Pushfit vs Solvent Weld for 110mm Soil Pipe

When to use pushfit

Pushfit is the correct choice for above-ground soil systems in domestic properties. The rubber ring seal accommodates thermal expansion — 110mm uPVC pipe expands by approximately 0.5mm per metre per 10°C change in temperature. Without this movement allowance, rigid solvent-welded systems crack at joints in cold weather.

Pushfit fittings also allow dismantling for maintenance, blockage clearance, and future extensions. This is particularly important on soil stacks serving multiple floors where access for rodding must be preserved.

When to use solvent weld

Solvent cement is used for below-ground drainage systems (usually 110mm or 160mm HDPE/uPVC buried underground) and where pipework is permanently concealed in concrete or render. Above-ground runs that will be accessible — in ducts, voids, or boxed-out areas — should remain pushfit for future access.

Note: 110mm above-ground fittings (pushfit, grey/black) are not interchangeable with underground drainage fittings (solvent weld, orange/cream). The sealing systems are different.

Grey vs Black 110mm Fittings

Both grey and black 110mm fittings are made from uPVC and have identical pressure and flow ratings. The difference is UV resistance:

• Grey — standard internal use, protected roof spaces, ducts. Not suitable for prolonged UV exposure (yellows and becomes brittle).
• Black — UV-stabilised, for external soil stacks, exposed pipework on building facades, or any run that receives direct sunlight.

Where a soil stack exits through an external wall and runs down the face of a building — common on terraced houses without internal stacks — use black fittings throughout the external section. Grey fittings can be used inside the building up to the point of exit.

Planning a 110mm Soil Stack Installation

Sizing and falls

Above-ground soil pipe typically uses a near-vertical stack (less than 5° from vertical) with branches connecting at 92.5° for WC waste. Horizontal branch runs should be kept as short as possible (maximum 6 metres from WC to stack for 110mm pipe) and must fall at 18mm per metre minimum (1:56) or up to 90mm per metre maximum (1:11).

Outside this range, self-cleansing velocity is not maintained — too flat and solids settle; too steep and the liquid outpaces the solids, leaving them stranded.

Air admittance valves vs open ventilation

The soil stack must be ventilated to prevent siphoning of traps. Two options:

• Open vent pipe — stack terminates above roof level with a cowl, at least 900mm above any opening window within 3 metres (Building Regs Part H).
• Air admittance valve (AAV) — where an open vent is impractical (flat roofs, loft conversions), a Durgo-type AAV can be used. It must be fitted in an accessible, ventilated location. Check local Building Control — some require open vent on the primary stack even when AAVs are used on branch runs.

Access and inspection points

Fit an access plug or rodding eye at the base of every soil stack and at each change of direction on long horizontal runs. Building Regs Part H requires access at every junction where a blockage cannot be cleared from a terminal point. Aquaflow socket plugs serve this purpose — they push in to seal and pull out for rodding.

Common Fittings Reference

Fixing and Support

Support 110mm soil pipe at maximum 1.2 metre intervals on vertical runs and 0.5 metre intervals on horizontal runs (BS EN 12056 guidance). Use pipe clips with rubber inserts to reduce transmitted noise — important on internal stacks in timber frame or masonry party wall construction where Building Regs Part E (sound) applies.

On vertical stacks, one fixing per storey should be a fixed point bracket that prevents vertical movement; other fixings should be sliding/guide brackets that allow thermal expansion. This is critical on tall stacks — a 4-storey run of 110mm pipe can move 8mm vertically between summer and winter.

Water Testing a New Soil System

Before concealing pipework, test the system with a water test: fit socket plugs to all lower openings, fill the stack with water to the highest point, and check for leaks at all joints over 30 minutes. Building Control may require a test certificate before signing off Part H drainage works.

Use the Aquaflow pushfit socket plugs as test plugs — they seal adequately for a static water test. For pneumatic air tests required on commercial projects, use dedicated inflatable test bags.

Related Guides

• Waste Pipes and Traps — 32mm and 40mm Push-Fit, Solvent Weld, and ABS Fittings
• Toilet Cistern Maintenance — Fill Valves, Flush Valves, and Pan Connectors
• Flexible Tap Connectors and Isolation Valves
• Wet Underfloor Heating Systems — Manifolds and Pipe Layouts
• Bathroom Extractor Fans — Humidity Sensors, Timers, and Part F Compliance