What is a Septic Tank?

Septic tank cut away

A septic tank collects and treats wastewater at a property that is not connected to the mains sewer system and is, therefore, most commonly used in rural areas.  The term ‘septic’ means ‘infected with microorganisms’; the tanks contain bacteria which break down organic waste.

The inclusion of a bacterial treatment mechanism is the difference between a septic tank and a cesspit, and these structures have both residential and industrial appliances.

Installed underground, a septic tank makes use of natural processes to treat the sewage it stores. Usually made up of two chambers or compartments, the tank receives wastewater from an inlet pipe.

How does a septic tank work?

Once sewage from a drainage system reaches a septic tank, the following occurs:

  1. Wastewater enters the first chamber
  2. The wastewater separates over time. Solids settle at the bottom, while oils and greases form a layer of scum at the top, leaving a layer of relatively clear water remaining in the middle.
  3. Clarified wastewater enters the second chamber. It then exits via an outlet pipe into a septic drain field, also known as a seepage field or leach field
  4. The remaining scum and solids in the tank are broken down by naturally occurring bacteria and what is left should be professionally removed periodically.

After the, now treated, sewage exits the septic tank, it is released via pipes into the ground. Legal limitations exist on how much sewage can be discharged into the environment per day, and these limitations vary based on whether sewage is pumped into flowing water (5,000 litres) or directly into the ground (2,000 litres).

A special permit is required to surpass these volumes, which can be obtained through contacting the Environment Agency on 03708 506 506;

Septic Tank maintenance advice

Septic systems require relatively little maintenance, but septic tank owners need to observe certain rules to make sure the tank system operates effectively.

For example, the following items should never be flushed down the drain or toilet (see The Dirty Dozen):

  • Food waste
  • Fat, oil and grease
  • Plastic bags
  • Nappies
  • Sanitary towels, including tampons, applicators and wrappers
  • Cotton buds
  • Condoms
  • Bandages and plasters
  • Baby wipes
  • Medicines, needles and syringes*
  • Cleaning wipes
  • Razor blades

These items will block the inlet and outlet pipes, and also disrupt the biological separation process taking place within the tank itself.

Frequent de-sludging is important to ensure a build-up does not occur. Annual maintenance should focus on removing solids from the tank- and should only ever be carried out by a qualified sewage worker. Similarly, disposing of this waste should be conducted by a registered waste carrier.

Another general maintenance guideline is to avoid using an excessive amount of anti-bacterial agents. These agents can affect the flora needed to process the waste water, which may hinder the septic tank’s function.

Septic drain field treatment

Similarly, a few simple rules will keep septic drain or leach fields healthy:

  • Protect the drain field by not covering it with structures, tarmac or contract
  • Avoid planting trees or plants on the area, as their roots can damage the underground pipes
  • Sow grass to help it absorb any discharged water
  • Prevent anyone driving or parking over the field

More advanced maintenance tips include designing the drain field in such a way to avoid overloading it with rainwater. This can be done by channelling roof gutters and surface drains away from it, as well as reducing general water use within the property. Facilitating proper septic tank drainage is essential; both for the environment and to protect the property owner from any legal repercussions associated with poor practice.

Emptying septic tanks

The sludge that remains at the bottom of the tank after the natural biological separation process has occurred, must be removed from the tank by a vacuumation truck.

Vac truck on grass

How often it needs emptying depends on a range of factors, from the size of the tank to the amount of waste that is added to the tank, and other variables. Some need emptying every couple of years, while others can go for decades before needing to be emptied. Most manufacturers recommend emptying annually.

Recent legislation (2019) affecting septic tank emptying dictated that owners of septic tanks that discharge water directly into canals, ditches, or general surface water, must have replaced or upgraded their drainage by the 1st January 2020.

When considering the cost of septic tank emptying, first ensure that your property meets all regulations and legal requirements have been met. The size and use of the property along with occupancy all contribute to the scoping of the correct septic tank installation.