Fragile Earth

Septic Tanks Explained


Every household in the UK produces large amounts of waste water. This consists of all of the water from sinks, baths and showers, the water that drains from the washing machine and the dishwasher, and of course, the waste that is flushed away every time you use the toilet. For town and city dwellers this is something that almost requires no thought, unless something gets blocked, as all of this liquid goes down the drains and into the sewage system. There is a proportion of every water supply bill that accounts for this. However, those who live in the country may be not connected to a sewage system and therefore need to make other arrangements. In the majority of cases this will take the form of a septic tank.

How does a septic tank work?

The waste water from the house goes into a tank where it settles, so that the liquid is separated from the solids. The waste water is mostly organic and both this and the solid matter is broken down and made harmless by bacterial action. Fragile Earth Septic Tank treatment, available in liquid and powder form can be added to the tank to boost naturally occurring bacteria. The liquid will leach away into the ground. The remaining solid matter will build up, and over time, perhaps annually, a contractor will come in and pump out this matter and clean the tank. However carefully the tank is managed, this will involve a certain amount of unpleasant odour.

The modern septic tank

Most modern tanks are made of plastic or fibreglass. Pipes take the influent from the house into the tank. If you could look inside your septic tank, you would find three layers. The top layer is the scum layer where organic material floats to the surface. Bacteria in the septic tank biologically convert this material to a liquid. The middle layer is the effluent layer where mostly clear water (although it does have some suspended solids in it)is found. The bottom layer is the sludge layer. This is the layer is where the inorganic or inert solid materials and the by-products of bacterial digestion sink. When the next batch of influent comes into the tank it will displace only the clear water. This function may be carried out by a secondary tank, but whatever happens it is important that the influent remains in the tank for a minimum of 24 hours before going to the soakaway.

The soakaway

The clear water, which is known as effluent, feeds into the soakaway via a pipe or pipes, passing first into a leach field typically filled with gravel or stone chippings. Once beyond this, the effluent will soak away into the soil. Obviously the amount of water that will be absorbed depends upon the type of soil in the area.


This will be calculated depending on the size of the house and the likely number of occupants. The calculations must be made carefully as too small a system will not cope and the waste water will back up, leading to potential blockages.

Dos and don’ts

  • There are some simple rules to follow to keep the septic tank working efficiently:
  • Remember that the system works based on bacteria breaking down the contents.
  • Try to use as few detergents, bleach or chemicals as possible as these are harmful to the bacteria.
  • There are bacteria friendly products and these should be used where possible, along with Fragile Earth Septic Tank treatment which will boost the bacteria.
  • Do not put fats or grease down the sink. This is also good advice for those connected to the mains sewers as solidified fats are one of the main reasons that pipes get blocked.
  • Do not put any solid materials into the system, other than naturally occurring ones!
  • This means no nappies, sanitary towels, cotton wool or condoms. Bag it and bin it.
  • You cannot connect rainwater downpipes to the septic tank system, it will overwhelm it and then the same problems will occur as with too small a tank.
  • The effluent must only go into the soakaway, never into a water course. Unless this has been approved by the Environment Agency you are committing a crime.
  • Read more at the website.