Septic tank
In the United States, the 2007 American Housing Survey indicated that about 20 percent of all households rely on septic tanks, and that the overwhelming majority of systems are located in rural (50%) and suburban (47%) areas. Indianapolis is one example of a large city where many of the city's neighborhoods still rely on separate septic systems. In Europe, septic systems are generally limited to rural areas.
Hyde Park Obelisk
There are two types of sewer vents within the Sydney Water system; educt and induct. Induct vents draw air into a sewerage system to areate the pipelines. Educt vents allow gases to escape when the gas is lighter than air. The shape of the cowling on the older types of vents were set to produce either eduction or indcution whenever there is a natural breeze. This is an educt shaft, a simple masonry shaft modelled on Cleopatra's Needle (now situated on the Thames Embankment, London) and erected in 1857 during the period of George Thornton as Mayor of Sydney. Vents are for the safety of personnel as well as to prevent corrosion by chemical decay. The ventilation of sewers is a very important facet of continued operation of a sewerage system. Poor ventilation can result in serious odour problems and breakdown in fabric.