Drainage A to Z

A helpful jargon busting guide to commonly used drainage terms.

Buchan Trap
A clay device located in a domestic drain that was installed in thousands of homes from 1870s to 1930s to prevent sewer air or rats from entering the property. This was in the belief that Cholera disease was spread through the air and that rats couldn't swim. Wrong on both counts! They are very prone to blocking and serve no purpose. Also known as Bristol interceptor or Croydon trap!

A covered tank usually below ground for storing sewage. They need regular emptying as the system is not subject to bacterial decomposition. Properties not connected to the main sewer typically use these, but septic tanks are now preferred as cesspool emptying costs have risen.

These take liquid waste only, usually from waste pipes and storm water 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.

Inspection Chamber
An inspection chamber offers access to equipment to carry out any drain inspections, but is smaller than a manhole, so offers no access for a drain engineer.

Interceptor Trap
These were 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 no longer installed 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.

Similar to drain relining (see below), but used for repairing isolated defects or small damaged areas within a drain, sewer or pipe.

Pitch Fibre
Pipe material that was used in the 1940s to 1970s as a cheaper and lighter alternative to traditional clay pipes. Unfortunately pitch fibre has a life span of 40 years, before it starts collapsing and becoming misshapen. So most pitch fibre has had its time. Depending on the condition, relining may work, but excavation and replacement may be necessary.

Drain relining is a cheaper, quicker way of repairing a drain or sewer. A new pipe is created within the existing one, without the need to excavate. A flexible liner impregnated with resin is pushed through the drain. This is then inflated to mould the resin to the pipe. The liner is heated, and once cooled will mould exactly to the sides of the original pipe.

Rodding Eye
A rodding eye is a small removable cover on a drain pipe that allows access to remove an obstruction using drain rods.

Root Ingress
Roots from trees will infiltrate small cracks or weaknesses in a drain pipe. They will restrict and eventually block the the drain. Root ingress can be removed by use of heavy duty root cutting equipment or high pressure water jetting. Depending on the condition of the drain, once the root ingress has been removed, the existing pipe work can be relined to prevent further root ingress.

They are used to store the immediate surface water run-off from hard surfaced areas, such as roofs or car parks, and allow for infiltration into the adjacent soil. Traditionally they have been used as a way of disposing of surface water in areas that are remote from public sewers.

Most houses with upstairs bathrooms have soil and vent pipes (SVP). 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.

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