Precast Concrete Siphon Septic Tanks – Absolute Concrete

Precast Concrete Siphon Septic Tanks

Absolute Concrete have been producing septic tanks for over 30 years. Historically these were made of layered plaster but recent concerns around contamination of ground-water and even potable water supplies has lead to the development of a large (One Size fits most) precast solid concrete design.

These are primary treatment units which means:

  • No Power Required
  • Low maintenance
  • Low ongoing costs.


Absolute Concrete have been producing septic tanks for over 30 years.  Available in plastered form or in recent times, more commonly in pre-cast format. They are simple, reliable and cost effective solutions for your septic waste. Our precast units hold roughly 4,500 litres and weigh close to 4.2 Tonnes and can be Hi-ab’d straight into a prepared hole. Precast concrete tanks provide a much greater density wall format that is much less likely to leach black water that can contaminate ground water.

Septic tanks are manufactured to NZS3107:1997 and are designed to be buried with a maximum of 600mm fill cover.

4,500 litre Single Chamber Tank

Certain septic tanks designs include siphons or other methods of increasing or decreasing the volume and  velocity of outflow to the drainage field.  This helps to load all portions of the drainage pipe more evenly and extends the drainage field life by preventing premature clogging. Absolute Concrete manufacture Siphon Septics incorporating the “Super” siphon or the equally popular “Flowking” siphon.  Each tank should also include a filter to prevent solids entering the siphon chamber.

These tanks are also ideal for storm-water attenuation, especially on sites where room is restricted.

Gravity fed dosing siphon.



We also manufacture a range of mini stand alone pump chambers that can be used to convert existing single chamber septic tanks into dosing or pump out systems.

Please call us for more information.