Waste Pipes & Fittings Buying Guide: 32mm, 40mm & 110mm Systems

Waste pipework looks simple until you have to choose between 32mm, 40mm and 50mm pipe, push-fit and solvent-weld systems, soil pipe, overflow fittings and the correct bends or traps. Mixing incompatible systems or choosing the wrong diameter can cause leaks, poor drainage or an installation that is difficult to maintain.

This UK waste pipes and fittings buying guide explains the main pipe sizes, push-fit versus solvent-weld waste, 110mm soil pipe, overflow systems, fittings and the practical checks to make before ordering. Browse our full waste and pipeworks range while you plan the installation.

Waste pipe vs soil pipe

Waste pipe carries water away from appliances such as basins, sinks, baths, showers and washing machines. Soil pipe is larger and is used for toilet waste and the main connection to the drainage system. In UK domestic plumbing, waste systems commonly use smaller diameters such as 32mm and 40mm, while soil systems commonly use 110mm pipe.

These systems connect together at appropriate branches, bosses or adaptors. Do not try to force a smaller waste pipe directly into a soil fitting without the correct connector.

32mm waste pipe

32mm waste pipe is commonly used for smaller sanitary appliances such as washbasins. The exact installation should follow the appliance and drainage design, but 32mm is a familiar size for bathroom basin waste runs.

Our range includes fittings such as a 32mm waste to overflow reducer for specific transitions. When buying 32mm pipe and fittings, make sure every component uses the same jointing system because push-fit and solvent-weld ranges are not automatically interchangeable.

40mm waste pipe

40mm waste pipe is widely used for baths, showers, kitchen sinks and other appliances with higher discharge rates. Products such as the 40mm push-fit waste swept bend provide directional changes while maintaining a smoother flow path than a very tight elbow.

The correct pipe size should suit the appliance, run length and drainage arrangement. If you are replacing an existing section, check the actual outside diameter and system type rather than relying only on a nominal description.

50mm waste pipe

50mm waste pipe can be used where greater flow capacity is required or several waste connections combine, depending on the system design. It is less common for a simple single basin but can be useful on longer or more heavily loaded waste runs.

The Davant solvent-weld waste pipe range includes multiple nominal sizes, giving installers a consistent solvent-weld system for different applications.

Push-fit waste pipe

Push-fit waste pipe uses ring-seal fittings that grip and seal the pipe without solvent cement. It is quick to assemble, can be easier to dismantle for alterations and is popular for accessible domestic waste runs.

The pipe must be cut square, deburred and inserted to the correct depth. Damaged seals, dirty pipe ends or poorly aligned fittings can cause leaks. Lubrication should only be used where recommended by the manufacturer.

Solvent-weld waste pipe

Solvent-weld systems use a compatible solvent cement to chemically bond the pipe and fitting. Once cured, the joint is permanent and cannot normally be dismantled without cutting the pipe.

Solvent-weld pipe is widely used where a rigid, permanent installation is preferred. It can be particularly useful for concealed runs, but careful dry fitting and marking are essential because the joint cannot be repositioned after the solvent has set.

Push-fit vs solvent weld

Push-fit waste is faster to assemble and easier to alter. Solvent-weld waste creates a permanent bonded joint and is often preferred where movement should be minimised. Neither is automatically better for every job.

The important point is compatibility. Push-fit and solvent-weld pipe can have different outside diameters even when both are described by the same nominal size. Use connectors specifically designed to transition between systems rather than mixing fittings directly.

Waste pipe bends

Bends change the direction of a waste run. Common angles include 90 degrees, 92.5 degrees and 135 degrees depending on the range. Where space allows, swept bends can improve flow and reduce the risk of blockage compared with abrupt changes of direction.

Examples include the FloPlast push-fit waste bend and 135-degree waste bend. Plan the route before ordering so you know the quantity and angle of each fitting required.

Waste couplings and tees

Couplings join two lengths of pipe in a straight line. A push-fit waste coupling is useful for extending or repairing a compatible pipe run.

Tees connect branches into a main waste pipe. The FloPlast push-fit waste tee is one example. Branch orientation and fall should be planned to encourage smooth drainage rather than creating opposing flows or flat sections.

110mm soil pipe

110mm soil pipe is commonly used for WC connections and soil stacks. Ring-seal push-fit soil systems allow pipe and fittings to be assembled with sealed sockets, while solvent-weld soil systems create permanent bonded joints.

Soil pipe installations need correct falls, ventilation and access for maintenance. External soil stacks also require appropriate support clips and weather-resistant installation in accordance with the system guidance.

110mm soil bends

Soil fittings are available in several angles, including 92-degree and 135-degree bends. The 110mm ring-seal 135-degree bend can be used to change direction more gradually than a single sharp turn.

Use as few direction changes as practical and maintain access where blockages could occur. Multiple tight bends in a short run can make rodding and cleaning more difficult.

Soil pipe branches

Branches connect WC or waste connections into a soil stack. A product such as the 110mm soil branch tee provides a defined connection point within a compatible soil system.

Bossed soil fittings can also accept smaller waste pipes using the correct boss adaptor. Check the number and position of inlets before ordering because branch fittings are available in several configurations.

Overflow pipe

Overflow pipe is smaller than standard basin or bath waste pipe and is used for warning or overflow connections from cisterns, tanks and similar equipment. 21.5mm overflow systems are common in domestic applications.

Our range includes 21.5mm overflow pipe plus couplings, bends, tees and tank connectors. Keep overflow systems separate from ordinary waste fittings unless an approved reducer or adaptor is used.

Traps and wastes

A trap holds a water seal between the appliance and drainage system to help prevent foul air from entering the room. Basin, sink, bath and shower traps are available in different depths and configurations.

When choosing a trap, check the waste outlet size, available space beneath the appliance and connection to the waste pipe. Vanity drawers and shallow shower trays can restrict the depth available, so compact or specialist traps may be needed.

Waste pipe fall

Waste pipes need a suitable fall so water and solids move toward the drain without leaving standing water. A run that is too flat can drain slowly, while an excessive gradient can also create poor performance in some layouts.

The correct fall depends on pipe size, run length and drainage design. Use the project or manufacturer guidance, support the pipe at the recommended intervals and avoid low spots between clips.

Cutting waste pipe

Cut plastic waste pipe square using a suitable saw or pipe cutter. Remove burrs and sharp edges before inserting the pipe into push-fit seals or solvent-weld fittings. An uneven cut can reduce insertion depth and make alignment harder.

Dry-fit the run before making permanent solvent-weld joints. Mark fitting positions so elbows and tees remain aligned when the cement is applied.

Expansion and movement

Plastic pipework expands and contracts with temperature changes. Long hot-water waste runs can move noticeably, so pipe clips and joints should be installed in a way that allows the system to accommodate normal movement.

Push-fit sockets can provide movement where designed for it, while solvent-weld systems may need expansion provisions elsewhere. Follow the manufacturer's installation instructions for long runs.

Waste pipe colours

Waste and soil systems are commonly available in white, black, grey and other colours depending on the product range. Colour can matter where pipework remains exposed, but it does not replace checking size and system compatibility.

Do not assume that two fittings are compatible simply because they are the same colour. Match manufacturer, nominal size, joint type and actual pipe dimensions.

Repairing an existing waste pipe

For repairs, first identify whether the existing system is push-fit, solvent-weld or compression. Measure the pipe and inspect how the joints are made. A slip coupling or universal compression fitting can be useful in certain repair situations, but it should be suitable for the pipe material and diameter.

If the existing pipe is cracked because of poor support or movement, repair the underlying cause as well as replacing the damaged section.

Waste pipes and fittings buying checklist

• Identify whether the run is waste, soil or overflow pipe.
• Confirm the required nominal pipe size.
• Choose push-fit or solvent-weld within a compatible system.
• Plan bends, tees, couplings and adaptors before ordering.
• Allow an appropriate fall toward the drainage connection.
• Include suitable pipe clips and supports.
• Check trap size and space beneath the appliance.
• Use approved adaptors when connecting waste pipe to soil pipe.
• Keep access for cleaning and maintenance where practical.

Frequently asked questions

What is 32mm waste pipe used for?

It is commonly used for smaller sanitary appliances such as washbasins. The final pipe size should follow the drainage design and appliance requirements.

What is 40mm waste pipe used for?

40mm pipe is commonly used for baths, showers and kitchen sinks, where discharge flow is generally higher than from a basin.

Can push-fit waste connect to solvent-weld pipe?

Not directly in every case because the outside diameters can differ. Use a suitable adaptor or universal connector designed for the two systems.

What size is toilet soil pipe?

110mm is a common UK soil-pipe size for WC connections and soil stacks. Check the existing installation and compatible fittings before ordering.

Shop waste pipes and fittings online

Browse waste pipes and fittings including 32mm and 40mm waste systems, 110mm soil pipe, push-fit fittings, solvent-weld components and overflow pipework. Match the diameter and jointing system throughout the run before ordering to keep installation simple and reliable.