Septic tanks rely on microorganisms to decontaminate the water. These are usually made of concrete and fiberglass with an in-out pipe system. These septic tanks are important in the septic system where sewage is treated naturally by holding its contents long enough for solids and liquids to separate. These things can only be found in areas that lack connection to main sewage pipes that the government had provided. They could be found built in suburbs, small towns, and rural areas and are not suitable for densely built cities.