Septic Systems


Have you recently inspected your septic tank and discovered it’s not working the way it should be? Or are you looking to upgrade your current septic system? O’Brien Plumbing Tamworth can help!

Our septic system services include:

  • Septic Tanks
  • Absorption Trenches

O’Brien Plumbing Tamworth provides supply, installation and maintenance of septic systems for domestic and commercial requirements, serving clients Tamworth and surrounding regions including Armidale, Gunnedah and Narrabri.

Septic Tanks

Septic tanks may be used to serve installations where the effluent can be disposed of through absorption trenches.

When sewage enters a septic tank, an equal volume of liquid is discharged from the tank. The primary purpose of the septic tank is to condition the sewage so that the discharged liquid will not clog the disposal system.

A septic tank combines two processes. Sedimentation takes place in the upper portion of the tank, and the accumulated solids are digested by anaerobic decomposition in the lower portion. As sewage from a building enters a septic tank, its rate of flow is reduced so that the heavier solids sink to the bottom and the lighter solids including fats and grease rise to the surface. These solids are retained in the tank and the clarified effluent is discharged. With good care and efficient operation, removal of solids maybe as high as 60 per cent, but at times the solid content of the effluent may equal or exceed that of the influent. Clogging of the disposal system will vary directly with the amount of suspended solids contained in the septic tank effluent.

Septic tanks do not accomplish a high degree of bacterial removal. Although the sewage undergoes treatment in passing through the tank, this does not mean that the infectious agents will be removed. Hence, septic tank effluent cannot be considered safe. The liquid that is discharged from the tank is, in some respects, more objectionable than that which goes in. It is anaerobic and malodorous.

However, this does not detract from the value of the tank. Further treatment of the effluent, including the removal of pathogens, is affected by percolation through the soil. In order not to disturb the bacterial action of the septic tank, disinfectants and bleach must never be flushed down toilets connected to septic tanks.

Septic tank capacity should equal a full days flow plus an allowance of 15–25 per cent for sludge capacity. The minimum desirable size of the tank is 3000 – 4000 litres depending on the size of the load entering the system. A septic tank servicing an average size home of five people will need to be desludged every three to five years.

Absorption Trenches

The design of the system can be varied to meet most topographic conditions encountered, however all absorption trenches must be installed level, preferably using a laser level for the excavation.

Many different designs may be used in laying out subsurface disposal fields. The choice will depend on the size and shape of the available disposal area, the capacity required, and the topography of the disposal area.

Not all soils are porous enough to permit use of absorption trenches. First test the percolation rate of the soil in the proposed absorption area to determine the speed with which the settled sewage will pass into the soil. Also determine the total absorption area required to serve the installation adequately.

The required absorption area is determined by the soil percolation test. This test should be performed by qualified sanitary engineering personnel.

Once absorption trenches are constructed, all traffic must be excluded by fencing or posting to prevent crushing the trenching. Planting shrubs or trees over the field is not a good practice, because the roots will clog the trench voids. However, grass over the lines assists in removing the moisture and keeping the soil open.

Generally, the longer the absorption trench, the longer the system will last and the cheaper it becomes, per metre, to install.

Even a well designed and properly operating septic tank and absorption trench system will eventually fail if it is not maintained. Regular maintenance is essential in prolonging the life of your absorption trench and avoiding any costly repairs.

If a client wishes to reuse the water, or the absorption area is not conducive to this type of septic system, we recommend the installation of an aerated water treatment system (AWTS).

For more information or to discuss your requirements, please contact O’Brien Plumbing Tamworth.

Call us (02) 6765 3235


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