Septic System Basics - How Septic Systems Work

Septic systems are expensive pieces of equipment. In fact, for the majority of households, it will be the most expensive household fixture. Over 20% of US households rely on an onsite septic system to treat wastewater, solids and grey water from the house.

On this page you will find information on how septic systems work, the different types of septic systems, how to maintain a system, danger signs and frequently asked questions.

diagram of a septic system

What is a septic system?

There are two main components that make up septic systems, they are the septic tank and a leach field.


What is a septic tank?

For full detail on what a septic tank is, see the septic tank page for full information.


What is a leach field?

For more information on what a leach field or absorption field is see the leach field page for further information.


How do septic systems work?

All liquid effluent, human sewage and wastewater flows through the household plumbing system, out of the home via the main drain drainage pipe and the effluent enters into the septic tank via the inlet pipe.

The job of the septic tank is to partially decompose lighter solids and do the majority of the processing and effective treatment of the wastewater. This job is completed when the lighter solids (sludge) and heavy solids settle on the bottom and the scum accumulate into a scum layer (including grease and oils) forms at the top leaving a layer of water in the middle.

The semi treated liquid wastewater or effluent then leaves the tank via the outlet pipe which often has effluent filters fitted to ensure sludge and sewage remain in the system and only septic tank effluent flows via the distribution box into the soil absorption field.

The absorption field is an allocated area in the back yard where small perforated pipes enable the liquid wastewater to be distributed into the surrounding soil to naturally remove pathogens including coliform bacteria and the soil treat any further nasties. Once the surface water has dissipated it will naturally make its way to the groundwater under the earth.

That is how septic systems work, if you have any further questions on how septic systems work, see the frequently asked questions below.

Frequently Asked Questions

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