Septic tank
A septic tank is an underground chamber made of concrete, fiberglass or plastic through which domestic wastewater (sewage) flows for basic treatment. Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment"). Septic tank systems are a type of simple onsite sewage facility (OSSF). They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field which provides further treatment. However, groundwater pollution may occur and can be a problem.
Tank Stream
From Hunter to Bond Street the Stream is a semi-circular stone arch with a shallow V shaped floor for 35 metres (1500 by 3000mm). The 1790 cut tanks were originally located in this area, but are not thought to have survived. For the following 86 metres, below Australia Square, the original sewer has been replaced with concrete box-profile pipe (1220 by 1830mm), inserted during the construction of the Square in 1962. The Australia Square Tower basement houses the access to Tank Stream for public tours and as an inspection point for Sydney Water.