There are three components to a conventional Septic Tank System;

• 1. Sanitary plumbing fixtures which include; the toilet, kitchen sink, dishwasher, laundry trough, washing machine, shower, hand basin and any other unit connected to a drain that carries waste to the septic tank.
• 2. The septic tank.
• 3. The effluent disposal system.

The Septic Tank

A septic tank consists of a watertight receptacle, designed and constructed to receive sewage from plumbing fixtures in the building.  Its main role is to separate the liquid phase by sedimentation and it also provides digestion of the refined organic matter by bacterial activity.

Three distinct zones exist in the septic tank;

• 1. The sludge zone, where the heavier solid material settles on the bottom of the tank.
• 2. The scum zone, where the lighter residues of grease and soap float to the top of the tank.
• 3. The detention zone, the middle layer containing mainly liquid.

Odours

The septic tank functions correctly when the contents are alkaline.  This can be achieved initially by mixing 5kg of hydrated lime into a slurry and flushing into the septic tank through the toilet pan.  Lime treatment can be utilised at other times when acidic conditions occur inside the tank.  (Note: avoid lime coming into contact with skin and eyes, wear eye protection and rubber gloves when handling this material).

Offensive odours will also result from the use of strong chemical cleaning agents which will kill the bacteria inside the tank and thus cause the system to malfunction.  Always use cleaning agents that are labelled as suitable for use with septic systems.

Mosquito Control

An incorrectly maintained septic system is the perfect breeding place for mosquitoes.  This can be prevented by;

• Covering all vents with a non-ferrous mosquito proof mesh
• Ensuring covers on inspection openings, septic tank, pump chamber and effluent disposal system are sealed to prevent mosquitoes from gaining access.

The use of pesticides intermittently flushed through the toilet pan has been used as a method of controlling mosquitoes, this will not be necessary if mosquitoes are denied access.  An excess of pesticide in the tank can disrupt necessary bacterial action and cause the unnecessary discharge of pesticide into the environment and underground water.

Maintenance Tips

DO

• Use only soapy water or biodegradable cleaners to clean toilet and sanitary fixtures.
• Check the septic tank every two years to see if it requires desludging.
• Desludge the tank every 3-4 years. (More often if a food waste disposal unit is connected to the system).
• Use toilet paper that breaks down readily.
• Restrict food scraps entering the system.
• Restrict the quantity of water entering the system to a minimum.

DO NOT

• Attempt to disinfect the septic tank after desludging.
• Dispose of sanitary napkins, coffee grounds, tea leaves, cooking fats or oils, bones, disposable nappies or cigarette butts into the septic system.
• Subject the system to hydraulic shocks eg the simultaneous use of washing machines, dishwashers, baths and showers.

AVOID

• Use of strong caustic alkalis, oils, acids, bleaches and disinfectants.

Prohibited Discharges

No person shall permit or cause any of the following discharges to enter a septic tank system;

• Stormwater, including roof and rainwater overflow and surface drainage waters.
• Backflush waters from a swimming pool or water softener.
• Discharge/backflush from a spa bath/pool in excess of 120 litres, unless the system has been specifically designed to accommodate such loading.
• Disposable napkins, clothing or plastic sheeting.
• Trade waste.
• Petrol or other flammable or explosive substance whether solid, liquid or gaseous.
• Disinfectants or deodorants, antiseptic or germicide powders or liquids unless specified as being suitable for disposal into a septic tank.
• Guidelines for the care of the sub-surface disposal system

Reduce the amount of water discharging into the system by:

• Spending less time under the shower.
• Using less water in the bath.
• Using suds-saving cycle on the washing machine.
• Minimising water use when washing hands and cleaning teeth.
• Installing dual flush systems in toilets.
• Minimising water usage in the kitchen. Eg Hand wash dishes instead of using a dishwasher.
• Avoiding the use of food waste disposal units.
• Ensuring leaking taps are repaired immediately

Protect the sub-surface effluent disposal system from migrating surface and sub-surface waters by;

• Diverting roof, tank overflow and storm waters to the street water table or an area beyond the soakage system.
• Minimising washing cars or watering lawns or gardens adjacent to or above the disposal system.
• Installing a diversion trench on the high side of the disposal system to arrest and divert surface and sub-surface waters away from the disposal area.

Sub-surface soakage relies upon evapo-transpiration of the effluent from the surface.  It is therefore important to keep the area free of buildings, structures or other impervious coverings such as concrete paths or driveways.