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Your questions answered

When Can a Septic Tank be Used?

Septic tanks are mainly used in locations where tests have demonstrated the subsoil is suitable for the discharge and disposal of treated waste water, and where approval has been granted by the appropriate local authority, or exceptionally, where written approval has been granted by the Scottish Environment Protection Agency (SEPA) to discharge to a stream.

If a septic tank does not function properly it can cause an odour nuisance, flooding and pollution, which can result in additional expense for you. If you follow the simple tips outlined on this page you should experience trouble-free and cost-effective waste disposal.

How Does a Septic Tank Work?

The purpose of a septic tank is to treat waste water from your property which is generally not connected to the public waste water system. It is usually either a large rectangular box made of brick, stone or concrete, or a bottle-shaped plastic tank buried underground not far from the property it serves.

A septic tank works like a simple waste water treatment works and the treated waste water drains from the septic tank's outlet pipe to a soakaway (shown in the diagram below) or stream.

Typical Arrangement Diagram

Waste material (sludge) is allowed to settle in the tank and is digested by natural bacteria breeding in the tank. Over time this sludge builds up on the bottom of the tank. This sludge has to be removed regularly to ensure that the tank continues to work properly and to prevent the soakaway becoming choked.

How Often Does Your Tank Need to be De-sludged?

De-sludging should normally take place every twelve months. However, experience has shown that depending on the tank size and usage, this period may be extended, but it is not normally beyond two years.

If you know where the septic tank outlet drains to, check that the discharge is a light grey colour. If the liquid includes dark solid material or recognisable sewage solids, this shows that the septic tank needs de-sludging.


What Does a Septic Tank Look Like?

Diagram of Modern Septic Tank

Diagram of Tradition Septic Tank

Do I have Any Responsibilities?

If you own or use a septic tank, the quality of the discharge and its impact on the environment are your responsibility. You may be held accountable for any pollution caused by your septic tank. This area is regulated by SEPA who will give you advice if required.

You are also responsible for ensuring that:

  • Your septic tank is properly maintained
  • Your septic tank access lids are secure and in good working order.
  • Any drains to and from the septic tank, including the soakaway, are free-flowing and free from blockages.

If your septic tank isn't maintained properly they can fail and cause flooding and foul odours as well as health risks and pollution of water supplies - such as nearby wells.

What Should I Check if I'm Buying a Property Served by a Septic Tank?

If you are considering buying a house or other property served by a septic tank you should ask the vendor for the following:

  • Do you have evidence that the tank has been maintained and regularly de-sludged?
  • Is the septic tank in good structural order and is there any history of problems?
  • Is the soakaway functioning properly?
  • Is there any evidence of flooding or pollution?
  • Has SEPA approved any discharge to a stream?
As your building society or bank valuation report is unlikely to cover these aspects adequately we would advise you to arrange a site inspection which includes the drains, the septic tank and the soakaway which can be carried out by a competent surveyor.