Cesspools, Septic Tanks and Tracing Drains

There are two methods for dealing with sewage from houses that are not connected to the main sewer.

A cesspool is simply a lined hole in the ground where the sewage collects. In time, the pool becomes full and has to be emptied either by the local council or by a private firm. Many houses have cesspools as small as 2.25 cu m (500 gallons); a family of four could fill this in as little as a week. Current Building Regulations require a capacity of 18 cu m. Modern cesspools may be prefabricated from glassfibre or concrete rings and simply placed into an already excavated hole; old ones would be made of brick, carefully sealed so that the sewage cannot escape and water in the surrounding ground cannot get in.

A septic tank is in effect a small sewage works. In it, the waste is broken down by bacteria until it is liquefied and rendered harmless: the resultant liquid can be disĀ¬posed of into a ditch or stream. Usually two different chambers are needed in a septic tank: in some cases the second chamber which contains a filter bed can be dispensed with and the half-treated sewage filtered through the sub-soil via land drains.

A well-constructed septic tank should need little maintenance apart from a periodic (say once a year) emptying of sludge. It is important not to use excessive amounts of disinfectant or detergents in the house, otherwise the bacteriological action could be slowed down and the tank clogged up.

Rain-water often drains into a soakaway. This can be a hole in the ground of one or two cubic metres capacity filled with rubble. The hole can be lined with bricks laid dry and covered with a close-fitting concrete slab. Rain-water drains into this hole and in time soaks away into the surrounding ground.

Tracing drains
Tracing the layout of a drain system is fairly simple – provided you remember that there should be an inspection chamber at all junctions and bends and that drains should run in straight lines between the chambers.

By pouring water down the various fittings in the house, it should be possible to determine which waste pipe connects to which drain and where each branch drain connects to the main drain. Fluorescent drain dyes can be used as an aid, if necessary. Any drains that do not show water after this test may be connected to a neighbour’s drainage system.

A plan with the deeds of the house may also show the layout of the drains; or the local council may know.