Waste pipe
Article under construction
Sizes
The (nominal) sizes of waste pipe used for domestic houses are
- 21.5mm
- 32mm (aka 1.25")
- 40mm (aka 1.5")
- 50mm (aka 2")
The actual pipe sizes vary a little between brands. The main variation is that solvent weldable pipe is one size, and non-weldable pipe for compression fittings is almost the same size, but not exactly. Just to be helpful to DIYers, both types are described using exactly the same size descriptions.
Uses of the sizes:
- 21.5mm - overflow pipe from cisterns, not used for sink waste
- 32mm - for 1 or 2 sinks, washing machine, etc
- 40mm - can service several appliances
- 50mm - for more than 4 appliances
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, and there's no legal or (usually) practical requirement to bring existing installs up to the most recent building regs.
Larger sizes also exist, and are used in flats and large houses.
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
- Not been in widespread use long enough to establish a proven long reliable service life
- Some are easy to remove
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.
Blockage prevention
1. Correct fall 2. Straight as possible runs, minimise the of use right angle joints 3. Enough access points to enable rodding the full length of the pipe. 4. Avoid putting any cooking fat or solids down the sink
Badly designed pipework with very poor flow is occasionally seen. With this, an occasional flush can help reduce solids build up, lesening 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.
Unblocking
Cutting
The main ways to cut plastic waste pipe are:
- Plastic pipe cutters - these look like giant secateurs
- Saw - most types will do it.