Drain Pipe materials
Salt Glazed Clay
This is the oldest type of pipe. These were typically made in 600mm lengths and jointed with spigot and sockets filled with cement. We often find that although the pipe itself is in good condition salt glazed clay drains often fail water pressure testing as the cement joints disintegrate over time.
A modern clay pipe which is still used and specified by Water Companies. Usually produced in 800mm lengths and jointed with plastic collars. The joints are far better than spigot and socket but do not offer flexibility as with the rubber joints used with uPVC pipe. Lighter in colour than salt glazed clay.
This material was used in the 1960’s and 1970’s instead of clay. It was favoured because of it’s lightweight meaning it could be delivered and installed in long lengths meaning fewer joints and easier installation.
Sometimes used in London where the drains run under houses from rear to front. It is very unusual for cast iron drains to leak but become corroded and then heavily scaled. Not used any more due to blockages and cost, particular the joints.
Lightweight, relatively cheap and easy to install with rubber joints designed to offer a degree of flexibility in the event of movement.
The photograph below shows the spigot and socket joints used on salt glazed clay and the rubber sealing joints used with modern uPVC
Key to drainage layout plan
These take liquid waste only usually from waste pipes. They consist of a grid to stop leaves entering over a hopper which is attached to a ‘u’ bend forming a water trap. The trap is designed to stop smells escaping from the drains.
RWG: Rainwater Gully
This is the same arrangement as a foul gully but takes water from a rainwater downpipe. A gully is used in place of a rest-bend when a rainwater drain connects on to a mains system.
RWP: Rainwater pipe
At the base of the downpipe below ground level there is a 90 degree bend to take the pipe from horizontal above ground to vertical below ground. These are used when the drain are not connected on to foul drains and typically go to soakaways.
SVP: Soil and vent pipe
The majority of houses with upstairs bathrooms will have soil and vent pipes. These pipes run up the side of the house (usually externally) and end close to roof level where they vent the drainage system to prevent a build up of smells. The waste pipes from the bathroom pass through the external wall and join the main pipe at first floor level.
In modern houses and flats there are often no gullies with all waste connecting on to the SVP. In the case of flats the downpipes are often internal.
RWP/TG: Rainwater pipe to ground
The downpipe discharges directly onto the ground with no below ground drainage.
VP: Vent pipe
The same as an SVP but it does not carry waste and acts merely as a vent. Typical use would be on a bungalow or a very large system which requires more then one vent.
A hole filled with rubble (usually brick rubble) designed to allow rainwater to escape away from the house. Used where there is no surface water or combined mains in the area or these are too far away. Modern soakaways do not use brick rubble as this greatly reduces their volume and so capacity and effectiveness. These should be no less than 3m from the building line and ideally a minimum of 5m.
Int Trap: Interceptor trap
These are a series of bends designed to form a water trap (similar to a U-bend beneath toilets), to stop smells and rodents escaping from the main sewer. They are installed just outside manhole chambers and there is usually a rodding access a few inches above the channel in the manhole which bypasses the trap for maintenance purposes. They are not installed any longer as they attract scale build up and over many years become blocked. The bends forming the trap make effective cleaning impossible and the rodding access bypasses the trap completely.
A ‘buchan’ or ‘running trap’ is the same as an interceptor trap but is not installed outside a manhole and often there is no sign from ground level that they are present. Often they have no rodding access so cleaning / accessing the drain beyond them is very difficult.
Where there is no mains drainage or it is too far from the house the foul drains may connect into a cesspit. These are large tanks which need to be emptied regularly.
Used where there is no mains drainage nearby. These tanks are not as large as cesspits and have outlets connecting to land drains (loose jointed or perforated drainage) or a soakaway or a combination of the two.
The most common arrangement is a system of two tanks. All waste enters the first tank (solid chamber) and solid waste sinks to the bottom. This displacement lifts liquids through an outlet into the second tank (liquids chamber). This in turn runs through the outlet into the land drain and soakaway. Modern installations are a single large chamber but still have separate compartments for solids and liquids.
In new houses it is unlikely septic tanks will be approved by the Environment Agency as they prefer ‘mini-treatment plants’. They are a similar size to modern septic tanks but the waste is treated sufficiently for them to discharge in to water courses as well as soakaways (following receipt of a ‘Consent to Discharge’ license from the EA).
Diagrams and pictures of drainage installations
Gully (taking foul waste pipes)
Gully (taking rainwater pipe ie., RWG)
4D.508 grid and hopper, 4D.500 trap, 4D.561 bend which connects on to straight length of pipe
Rest-bend at the base of a rainwater pipe,
vent pipe or soil and vent pipe
Picture of the vertical downpipe at ground level
4D.581 Long radius rest bend
Picture showing the vertical above ground part of a soil and vent pipe and the connection from the first floor bathroom
Typical septic tank
Tail drains from septic tank
Old style rainwater soakaway