Waste pipe

Pipe Sizes & Types

The (nominal) sizes of waste pipe used for domestic houses are

• 21.5mm
• 32mm (aka 1.25")
• 40mm (aka 1.5")
• 50mm (aka 2")

Uses of the sizes:

• 21.5mm - overflow pipe from cisterns, not used for sink waste
• 32mm - for 1 or 2 sinks
• 40mm - for washing machine, can service several appliances
• 50mm - for more than 4 appliances

Larger sizes also exist, and are used in flats and large houses.

In practice the waste pipe sizes above are sometimes found serving more appliances than is currently building regs compliant. This doesn't usually cause a problem.

There are 2 types of pipe, solvent weldable and non-weld. For a given nominal size,

• solv weld pipes are all the same real size.
• non-weld pipes are fractionally bigger
• exact non-weld pipe size varies a bit between manufacturers
• Just to be helpful, all these variations are described using exactly the same nominal size description.

• Solv weld pipe is for solv weld fittings
• Non-weld pipe is for pushfit fittings
• Compression fittings usually fit both types of pipe

Fall

Least tendency to deposit solids occurs with a fall of -. New pipework should have a fall of - to - to comply with building regs.

Occasionally waste pipework is seen that flows uphill. Water isn't so keen on going upwards, and such arrangements tend to either not work or collect solids and be prone to blocking.

Types of fitting

Solvent weld

• small & slim
• cheap fittings
• use solv weld pipe only, the other type wont fit or weld
• undoing a solvent weld is completely impossible, the plastic fuses together becoming one piece
• To fit, wipe the fitting and pipe clean, brush on pipe weld solvent, assemble the joint and let it set. If the pipe isn't clean, use a scourer first
• Solv weld piping soemtimes lacks access points, as no joints can be undone. Where access is needed, an access point can be included (or even a compression or pushfit tee, if preferred).

Compression

• bulkier
• more money
• often these will fit all variations of a given nominal size of pipe, but not always
• undoable
• reusable if the rubber rings are ok
• check its watertight after fitting, as its possible for the rubber ring to sit wrong and allow leakage

Pushfit

• Quick & easy to use
• Some are easy to remove
• Generally won't fit solv weld pipe
• Joints are more easily pulled apart than other fitting types, so proper pipe support is necessary.

Compliance

New pipework must be building regs compliant at time of fitting. Old pipework need not legally meet any building regulations, current or past, and upgrades of such pipework are at the discretion of the householder. A lot of non-compliant pipework works satisfactorily in practice.

Blockage prevention

• Correct fall
• Straight as possible runs, minimise the of use right angle joints
• Enough access points to enable rodding the full length of the pipe.
• Where space permits, a swept bend is better than a sharp right angle
• Avoid putting any cooking fat or solids down the sink. Molten fat causes lots of blockages.

Badly designed pipework with very poor flow is occasionally seen. With this, an occasional flush can help reduce solids build up, lessening the risk of blockage. This is easily done by eg filling the sink at the beginning of the pipe run to the brim, and letting it flush the pipe.

Impending blockages are easier to clear than a blocked pipe, and can be spotted in 3 ways:

• sink drains very slowly
• outflow of pipework very slow (visible on old open drain systems)
• Trickling sound of pipework continues awhile after the sink etc is empty

Unblocking

Unblock a Drain

Cutting

The main ways to cut plastic waste pipe are:

• Plastic pipe cutters - these look like giant secateurs
• Saw - most types will do it.

Sawn ends need the outer burr trimming off with a knife.

Clips

Plastic pipes sag under the load of water easily, and should be clipped to the wall. Failure to do so results in sag, with poorer flow and tendencey for the pipe to pull out of its fittings.

Different types and brands of pie clips have differing pipe to wall spacing.

See Also

• Unblock waste pipe
• Paint waste pipe
• Water