How Does a Septic Tank Work?

Posted by Callum Vallance-Poole, on April 11, 2022.

Graf UK Carat Septic Tank

Septic tanks offer a fantastic solution for households that have poor drainage or who are not connected to the local sewer network. They ensure that household wastewater is disposed of safely and efficiently, without being harmful to the local environment. Here we explain what a septic tank is, how it works and how your home can benefit from one.

What is a septic tank?

A septic tank is a wastewater treatment system that breaks down waste received from a nearby property. Rather than sending the waste into the local sewage system, the septic tank helps to biologically decompose the waste before safely discharging it into the local environment where it can drain naturally into the soil via a soakaway.

The wastewater received by a septic tank in a domestic setting is sent from the plumbing system flushed from the bathrooms and kitchens. They are typically used by properties that are not connected to a mains sewage network in rural areas or that have poor drainage, allowing for wastewater to be disposed of safely.

A septic tank with a soakaway is constructed from various materials, including concrete or brick, although modern systems tend to be made from polyethylene or fibre glass. The internal design is simple, and the shape of the tank is usually either round or rectangular, with many tanks stored underground.

How does a septic tank work?

Previously, there were two ways in which a septic tank could work: with a soakaway and without a soakaway. However, changes to environment legislation at the start of 2020 meant that septic tanks without a soakaway (which discharges directly to a stream, river, pond or ditch) is no longer permitted. If you have a septic tank that still discharges in this way you will need to upgrade the infrastructure to avoid facing prosecution.

Waste solids produced from a property are sent to a septic tank for storage and safe disposal. Inside the tank there are usually a few chambers, which are connected to baffles or T pipes, while it will also have an inlet pipe and an outlet pipe.

The inlet pipe moves the waste from the house so it can be received by the tank. It remains in the tank long enough for the solid and liquid waste to be separated from each other. The drainage field is connected to the outlet pipe. The pre-processed wastewater moves out of this pipe into the soakaway or drainage field where it can slowly dissipate into the soil.

After a while the waste inside the tank will form into three layers: the first layer is made up of grease and oils, the middle layer contains wastewater and waste particles, and the bottom layer is the heaviest and contains thicker particles.

Inside the tank, naturally forming bacteria breaks down the solid waste so the liquids can separate and start to drain away efficiently. General maintenance will need to be carried out over time to clean away anything left at the bottom of the tank, because septic systems are only very basic forms of sewage treatment and are not able to fully self-clean.

To understand more easily how a septic tank works we have broken it down into stages:

  • Wastewater from the property leaves the main drainage system and heads towards the inlet pipe that is connected to the septic tank.
  • The septic tank receives the wastewater and stores it until the three layers start to form, with solids settled at the bottom, wastewater in the middle and grease and oil on top.
  • Once separated, the waste can then start to leave the tank through the outlet pipe into the drainage field or soakaway.
  • The wastewater exits the tank out into the drainage field where it settles onto the soil, and it can then start to filter downwards.
  • The soil naturally treats and disperses the water, which is known as percolating, and will eventually discharge to groundwater.
  • Harmful bacteria, nutrients and viruses are also eventually removed once the wastewater filters into the soil.

What are the benefits of a septic tank?

The benefits of installing a septic tank include:

  • Installing a septic tank means you won’t have to pay the local water board for connecting to the sewer network. The cost of this can be quite high, especially compared to installing a septic tank. So, if you live in a rural area where drainage isn’t particularly good, a septic tank is usually the most cost-efficient option.
  • If you want to improve the nearby environment, using a septic tank is a good option, as waste is not being transferred into the local water courses. Instead, the wastewater is sent into the soil via a soakaway. A septic tank also creates less pollution as the waste is not going into the sewer system and your carbon footprint will be lowered as you are not using mains sewage which costs a lot to run and process.
  • The installation of a septic tank also encourages better use of your drainage system at home. Toilets and sinks can often become the dumping ground for many unwanted items, which can wreak havoc in the plumbing. Knowing you have a septic tank receiving the waste will reduce the chances of dumping harmful chlorine-based products and items that could lead to drainage problems.

Septic tank maintenance tips

Taking good care of your septic tank will go a long way towards it lasting for longer and you getting better value for money. Some tips to bear in mind include:

Regularly inspection the tank

Do this every few months to check for damage to the tank, its components and the soakaway.

Soakaway protection

Avoid parking or driving over your soakaway and do not plant trees or plants nearby as root infiltration can become a problem.

Pump your septic tank

Pumping the tank every 1-3 years (depending on usage levels) will ensure it maintains a good level of performance. Use a specialist company for this as they will have the correct tools and equipment.

Manage your water output

If you can make your appliances more water efficient, this will lessen the strain on the septic tank, helping it to last longer. Whether it’s doing proper care and maintenance, or upgrading your appliances, there are lots of things you can do to become more water efficient.

Marketing Coordinator - Based at our UK HQ in Banbury, Oxfordshire, Callum is responsible for promoting Water Management Systems, Attenuation Tanks, Treatment Plants, Rainwater Harvesting Systems and more!