An On-site Wastewater Management System refers to any system that processes wastewater and disposes of the effluent by applying it to the land within the property boundary.

What is an On-site Wastewater Management System?

An On-site Stormwater Absorption System collects and disposes of rainwater (from roofs, driveways and other ground surfaces) within your property. If your home is not connected to the sewer, you may need to have an On-site Sewage Management System.

Septic tanks and trench style absorption systems are the most common type of domestic wastewater treatment systems in Australia.

Absorption Trenches

Absorption trenches are usually built below ground and the bottom layer is filled with a hard aggregate such as uncompacted gravel. Either perforated piping, self-supporting arch trenching or box trenching is placed in the trench and is backfilled with gravel. A geotextile filter cloth is then laid over the pipe and gravel and under the top soil to ensure that the soil does not penetrate and block the trench.

On-site Stormwater Absorption System Construction
On-site Stormwater Absorption System Construction
On-site Stormwater Absorption System Construction
On-site Stormwater Absorption System Construction

Effluent flows into the trenches where it is absorbed through the trenching material and into the surrounding soil. The absorption process and the action of bacteria in the soil treat the effluent.

If you are building a new home that requires an On-site Wastewater Management System or have an existing system that needs to be altered, All Line Plumbing are here to help!

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There are special regulations that apply to these On-site Wastewater Management Systems and as the owner of the property, it is your responsibility to ensure that the system is approved by your local council and is working efficiently and safely.

Types of Wastewater Around Your Home

Household Wastewater

There are 3 types of household wastewater:

  • Blackwater

    Wastewater generated from toilet plumbing fixtures and is heavily and directly contaminated with human faeces and/or urine and may contain contaminated solid material, such as toilet paper. This wastewater is highly infectious.

  • Greywater

    Wastewater from non-toilet plumbing fixtures and includes wastewater from hand basins, showers, laundry and kitchens. Greywater is often contaminated with human faeces, dirt and other materials but to a lesser extent than blackwater and is therefore considered less infectious.

  • Sewage

    Wastewater from the premises (both blackwater and greywater) normally discharged to a swewer and is considered very infectious.


Stormwater is rainwater as well as anything it carries with it such as water from roofs, roads, footpaths, driveways and other ground surfaces and can include sewage from sewer overflows.

Unlike sewage, stormwater has not been treated and the stormwater pipes carry all the water that flows into waterways inhabited by fish, frogs and other aquatic animals and plants.

How can Wastewater be disposed?


Through pipes called sewers into a sewerage system and treated in a single large sewage treatment plant.

It can then be converted into a resource for selective reuse for car washing, outdoor household garden watering, toilet flushing, golf course watering and irrigation of crops.

The treated effluent may also be discharged to rivers and oceans.


Through pipes into a local community small sewage treatment plant for local community reuse.

A number of these local systems make up de-centralised sewage management.

On-site Wastewater Management System

Where stormwater, sewage or components such as greywater must be partially or fully treated for utilisation or reuse within the property boundaries.

On-site single domestic wastewater management is regulated jointly by local councils and NSW Health.

On-site systems may not be installed or altered unless approved by the local council.

Do you require an On-site Wastewater Management System?

If your local council require you to have an On-Site Wastewater Management System on your new or existing property, contact us today. We can point you in the right direction to start the process of assesment, system design and approval and get your On-site Wastewater Management System installed.

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How does an On-site Sewage Management System work?

Your septic system treats your household wastewater by temporarily storing it in the septic tank where bacteria do the work of digesting waste. Fats and solids are retained in the tank and liquid effluent flows into the trench and is further treated by the soil.

The contents of a healthy septic tank should form 3 layers:

  • A layer of fats (called scum) which floats to the surface.
  • A clear layer (called effluent).
  • A layer of solids (called sludge or bio-solids) which sinks to the bottom.

When the tank gets too full, wastewater is gravity-fed or pumped from the septic tank/s into an absorption trench. Eventually the water evaporates from the soil, is absorbed or is taken up by plants growing on the absorption area.

On-Site Sewage Management System Problems

Clogged trenches are a common cause of septic system problems. Trenches fail when they get blocked and effluent is unable to evaporate or drain away.

You can tell if the trench has failed because the area will be soggy, smelly and covered with dense grass.

Other signs for On-site Sewage Management System issues include:

  • Odours outside the house.
  • Toilet does not flush easily and quickly.
  • Water goes slowly down drains.
  • Gurgling sounds in the plumbing.
  • Backup of sewage in house plumbing.
  • Tank has not been pumped out in the past 5 years or checked in the past 2 years.
  • Rampant weed growth downhill of the absorption trench.

Should you notice any of the above signs, contact All Line Plumbing immediately.

Badly maintained On-site Sewage Management Systems can:

  • Cause a serious health threat to family and neighbours.
  • Degrade the environment, especially waterways.
  • Reduce the value of your property.
  • Be very expensive to repair.

If you have absorption trenches don't wait until the trench starts to fail before having your tank pumped.

The NSW Government introduced the SepticSafe Program in 1998 to help property owners and Councils keep onsite sewage management systems working efficiently and safely. All owners of onsite sewage management systems are now required to apply to Council for an Approval to Operate (license).

More info: Office of Local Government

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