Septic tanks are used as pre-treatment units before the sewage enters the municipal sewage network or absorptive wells. The septic tanks can be used with simple or advanced systems depending on the quality of the wastewater requested. In most applications, simple septic tanks with at least one separating wall inside are used. In this septic tanks the inlet sewage settles in the first section and anaerobic bacteria break down most of the accumulated sludge. Also some of the floating materials remain in the first section and on the surface of the sewage. Wastewater then enters the second section, where secondary settling occurs, followed by the septic tank discharge.