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What breaks down sewage in a septic tank?

What is a Septic tank Sewage System?

Commonly used in rural areas without access to centralised sewer systems, a septic tank is essentially an underground chamber made from either concrete, fiberglass, or plastic which breaks down waste matter by the process of decomposition and drainage.

Septic Tank Diagram

A septic system generally contains the following functional parts:

  1. A Septic tank : this can be for all wastewater from a home, or for toilet discharge only A septic tank can also be a single tank or a multi chamber septic system
  2. A disposal area : this is usually a sand mound or a trench, as you shouldn’t discharge septic waste above ground
  3. A Grease trap : common in the commercial food industry and used to stop oil and grease going down the drain
  4. Drainage pipes
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How does a Septic Tank break down sewage?

A septic tank works by the simple process of biological decomposition and distribution drainage. Bacterial microorganisms break down the waste inside a septic tank which can then be safely redistributed or disposed off.

Septic Tanks and the sewage process

  1. All waste flows into the Septic tank. This can include all wastewater from a home, or for toilet discharge only
  2. This waste fills most of the tank and aerobic bacteria begin breaking down the organic matter.
  3. Broken down solids fall to the bottom of the tank creating a sludge layer of organic solids and the byproducts of bacterial decomposition.
  4. Some of the matter (ie. grease and fats) float to the top of the tank and form a scum layer.
  5. A filter prevents most solids from entering the outlet pipe.
  6. As new waste water enters the tank, it displaces the matter that's already there. This water flows out of the septic tank and into a drain field.
  7. The drain field is made of perforated pipes buried in trenches filled with gravel.
  8. Holes in the drain septic field pipe slowly allow the watery waste to seep into surrounding gravel.
  9. Gravel around pipes allows water to flow into soil and oxygen to reach bacteria.
  10. Aerobic bacteria in gravel and soil complete decomposition of the waste.
  11. Clean water seeps down into the groundwater and aquifer.


What breaks down sewage in a septic tank? Let our experts help you.

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    Because we are not a manufacturer and not tied to one particular system we can always offer the best solution for your wastewater needs.


    Because we do this every day we have developed a close knit expert team for every step of the process – from plans and council paperwork to excavations, electrical and plumbing. We handle it all to make the whole process as stress free and quick as possible.


    Most people have never installed a home sewerage treatment plant and don’t know the next step, that is why we offer a free 30 minute phone consult with one of our experts to point you in the right direction.


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    Not sure what system is right for you, or want to know if your system is working properly? Just give one of our friendly wastewater experts a call and they will be more than happy to help.


    We will always look to repair your system rather than replace it if it does not need to be, which will generally save large amounts of money sometimes up to and over $10,000.