WA's wastewater, Rainwater & Irrigation Professionals
Greywater Reuse Systems
Unit 1 / 18 Wandeara Crescent | Mundaring WA 6073

A septic tank is a watertight chamber, typically made of concrete or plastic, that is used for primary treatment. Wastewater flows from the whole house into the tank/s. Settling and anaerobic (without air) processes reduce solids and organics, but the treatment is only moderate.
The first tank or chamber holds gross solids, while the second tank or chamber allows sedimentation of some suspended solids before it passes into the leach field.
Septic Tank (GRAF)

Effluent (liquid) flows through the tank and heavy particles sink to the bottom, while scum (mostly oil and grease) floats to the top. Over time, some of the solids that settle to the bottom are degraded anaerobically. However, the rate of accumulation is faster than the rate of decomposition, and the accumulated sludge and scum must be periodically removed. 

After a short retention time (usually a few days to a week) the resulting effluent is discharged and infiltrates into the ground. Accumulating faecal sludge and scum needs to be removed from the chambers after 7 to 10 years and correctly disposed of by an authorised Liquid Waste contractor.

We have an Online Special: Residential Septic Tank Kits - 4,000L - non-trafficable


Over time, anaerobic bacteria and microorganisms start to digest the settled sludge anaerobically, transforming it into carbon dioxide (CO2) and methane (CH4 - biogas) and some heat. The gases produced during anaerobic digestion must be allowed to escape. 
The drainage system of the house has a ventilation pipe at the upper end, allowing gases to escape from the septic tank along the drains and through the vent.

Leach drains

A leach drain is a tube-like structure which is made of concrete or plastic and buried in the ground. There are holes in the sides. Its width can vary and its length depends upon the size of the leach drain being used, the amount of liquid waste to be disposed of, the type of soil (dirt) around it, and how it is built.

The liquid waste enters the leach drain at one end then slowly seeps down through the open base and out the sides through holes into the surrounding soil.

Under normal operating conditions, users do not come in contact with the influent or effluent. Many of the problems with septic tank systems arise simply because it is likely to contain large numbers of pathogens, which can be a potential source of infection. Effluent, scum and sludge must be handled with extreme care.

Advantages of septic tank systems

• No real problems with flies or odours if used correctly
• Simple and robust technology
• No electrical energy is required
• Low operating costs
• Long service life


• Constant and sufficient amounts of piped water required to bring the waste to the treatment unit
• Low reduction in pathogens, solids and organics
• Regular desludging must be undertaken
• Only suitable for low-density housing in areas with low water table and not prone to flooding
• Effluent and sludge require further treatment and/or appropriate discharge (at waste site)
• Relatively large land area required for tanks and drains.
• Other structures (e.g. main driveway, shed, garage, pergola) cannot be built on top of these. Access must be available at all times to clean and desludge.

The septic system functions by micro-organism activity and is designed to treat household waste and common substances introduced into the system. For the system to maintain optimum operation please read these notes carefully. 

Restricted limited use substances

The following substance can only be introduced into the unit in small to moderate amounts, otherwise it will disrupt the treatment process.

Avoid the excessive use of the following:

1. Laundry bleach (only as needed per load)
2. Harsh household cleaners (use in moderation)
3. Cleaning product for a toilet (do not use chemicals such as chlorine, or toilet blue.)
4. Mould killing products

Do not drain oils or fats

For disposal of any oil or cooking fat, soak the oil onto some paper and expel into a rubbish bin. Wipe all oils and fats from all cutlery and kitchenware before cleaning.

Do not drain any substances that do not decompose in water

• Diapers and sanitary goods do not decompose in water.
• Use only toilet paper that disintegrates easily in the water. Do not use tissue paper.

High use water devices

The draining of hot tubs and spas into the unit could cause temporary hydraulic overloading and may reduce the efficiency of treatment. Please drain these devices onto another location or release slowly in short bursts and re-plug each time.

Do not drain any harmful substances

• In general, if a substance is considered harmful to an individual then it should also be considered harmful to the system.
• The list below displays examples of harmful substances to the system. Do not introduce these items into the treatment system.


 Motor oil
 Brake fluid
 Paint thinner
 Solvents
 Herbicides
 Strong caustic drain cleaners
 Oils and body lotions
 Antifreeze
 Paint
 Gasoline
 Pesticides
 Strong disinfectants
 Toilet disinfection tablets
 Antibacterial soaps
 Deodorisers
 Preservatives

Food Products

 Coffee filters and grounds
 Fruit and vegetable peels
 Meat products
 Garbage disposal waste
 Greases or lards
 Seeds
 Bones
 Egg shells


 Sanitary napkins and feminine products
 Cigarette butts
 Paper products – e.g. paper towels and baby wipes  Plastic / rubber products
 Condoms
 Cat litter
 Dental Floss


Ideally, to start up a septic tank it should be "seeded" with sludge from a tank that has been operating for some time to ensure that the necessary microorganisms responsible for anaerobic digestionare present.

Septic tanks should be checked from time to time to ensure that they are watertight. Routine inspection is also necessary to remove floating debris such as coarse materials and grease, to ensure that there are no blockages at the inlet or outlet and to check whether de-sludging is needed.

It is very important to perform proper maintenance and cleaning in order to sustain the unit’s perfect condition. Regular maintenance inspections are to be undertaken in accordance with the wastewater treatment tank regulations.

Subject Time and Frequency

Diverter valve Quarterly. Change the diverter valve to allow water to pass into the other drain. Do this at the start of each season. e.g. first day of spring, summer etc. At worse, change the valve on your birthday.

Regular inspection 

Yearly – check for leaks at lid, growth of vegetation (roots) into tank, scum and sludge levels.
Removal of sludge ・Seven to ten years. Sludge pump-out is required if accumulation exceeds the holding capacity.
(Excess sludge and scum build-up is dependent on system loading.)


Manufacturer warrants, to the purchaser and subsequent owner during the warranty period, that the mechanical components to be free from defects in material and workmanship under normal use and service, when properly used and maintained for a period of two years. The tanks are guaranteed for a period of 15 years, both periods commencing from the date of purchase by end-users. Parts that inspections determine to be defective in material or workmanship will be repaired, replaced or remanufactured at Manufacturer’s option, provided however, that by doing so we will not be obligated to replace an entire assembly, the entire mechanism or the complete system. No allowance will be made for shipping charges, damages, labour or other charges that may occur due to product failure, repair or replacement.

This warranty does not apply to and shall not warrant any material or product that has been disassembled without prior approval from the Manufacturer. There will be no warranty granted if the tank system has been subjected to misuse, misapplication, neglect, alteration; that has not been installed, operated or maintained in accordance with Manufacturer’s instructions.

Water Installations also offers a two year workmanship warranty that relates to all work caried out by its employees or authorised contractors. 

Consultations & Quotations

It is best to schedule an on-site consultation where you will receive site specific, one-on-one expert advice.  Click here > 

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