Auckland septic tank 5400 litre two chamber. Sizes and dimensions vary to suit your specific dimensions and household needs. This custom built septic tank was to replace an old concrete septic tank in Taranaki, New Zealand. Light in weight, strong and to stand the test of time. Custom fabricated from 12mm High Molecular Weight Polyethylene (HMWPE) and we have a large range of septic tanks, septic treatment tanks and effluent tanks to suit your requirements, both local and international.