Septic tanks

This article discusses how your septic tank works, how to care for it and what products to use in it.

How does a septic tank work?

Woman wearing pink rubber gloves srubbing a toilet

Septic tanks function as a sedimentation tank and anaerobic digester, similar in principle to a primary sewage treatment plant. Sewage enters a holding tank (3000-6000L) where it sits for one to three days. During this time the solids fall to the bottom of the tank where they form sludge. The remaining liquid then flows out of the tank into pipes, which lead out to a field. The pipes have tiny holes to allow the liquid to trickle out into the soil where it is decomposed by soil bacteria. 

A septic tank, if functioning properly, poses no health risk. Most problems occur with septic tanks when they are overloaded. Knowing your load limits and adhering to them is advised. Therefore, it is important to understand your septic system and the correct products to use.

How should I care for my septic tank?

  • Do not use products that are highly corrosive. Products such as caustic soda should not be used to clean drains connected to septic tanks. If you need a powerful cleaner that is safe for use in a septic system, use a disinfectant like DOMESTOS.
  • Do not ignore your septic system. Good maintenance should ensure your system functions as it should. This includes activities such as: getting the sludge pumped out of your tank routinely, (approximately every three years) and repairing leaky fittings in the home, (to avoid overloading your tank). Avoid planting trees or other plants where they could grow over pipes which lead away from the septic outlet.
  • Do not overload the system. Each septic tank has a maximum daily capacity. Exceeding this can result in back-ups and surfacing of the contents.
  • Do not use garbage disposals Garbage disposals increase the loading of solids and can mean your system needs to be pumped more frequently.
  • Take care with what goes into the system. Never let items such as plastic film, tampons, etc. be flushed down the toilet. They can cause serious blockage problems in a septic tank.

What products can I use in my septic tank?

Septic tank owners can use all Unilever Australasia cleaning products. Normal household use of cleaning and washing products should not interfere with the correct functioning of the system. 

Even normal household use of disinfectants does not inhibit the bacterial action of the system because they dilute by the time they reach the septic tank. DOMESTOS cleaner is even better to use than disinfectant if you have a septic tank because its active ingredient gets used up by the soil and grease commonly found in household drains. However, it is important always to follow the directions for use on the packet/bottle to ensure you are using the correct amount for the cleaning task. 

The recommended Unilever Australasia cleaning products you can use are: OMO, PERSIL, SURF and DRIVE laundry detergents for clothes washing, COMFORT fabric softener for fabric conditioning, DOMESTOS disinfectant to disinfect and clean and JIF cleaner to clean surfaces. All Unilever Australasia's personal care products such as SUNSILK and DOVE can be used by people who have septic tanks.

Cleaning products for envirocycle or biocycle style systems

Aerobic wastewater treatment systems such as Envirocycle or Biocycle are a more recent invention. They differ from traditional septic tanks in that they consist of a series of chambers. We do not have years of research results assessing our products in these systems as we do with traditional septic tanks. Therefore, we can give you no direct advice on products to use. We can, however, pass on advice given to us by the manufacturers. Alternatively, you can contact the manufacturers directly.

According to the manufacturers of Envirocycle and Biocycle, it is safe to use biodegradable products in these systems. The manufacturers recommend that you avoid using the following type of products:

  • Antibacterial solutions
  • Caustic solutions like many oven cleaners and drain cleaners
  • Disinfectant and ammonia-based cleaners.

They also recommend that you avoid pouring large quantities (½ litre or more) of beer, wine, milk or fruit juice into the system.

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