Effluent sewer
Effluent sewers also currently serve fewer people than septic systems, which also use septic tanks, but simply dispose of the effluent by draining it into a leach field. About one quarter of United States homes dispose of their wastewater with septic tanks. However, effluent sewers are being looked at as a sewage treatment solution in areas where gravity sewer systems are not well-suited or when the high capital cost to build a gravity system is prohibitive. Areas that are less than ideal for gravity systems include areas that are large, but extremely flat and areas that require long-distance pumping, such as where homes are widely spread out or when several small villages or towns connect their sewage systems so that a centralized plant can be built.
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.