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.
Septic tank
The remaining impurities are trapped and eliminated in the soil, with the excess water eliminated through percolation into the soil, through evaporation, and by uptake through the root system of plants and eventual transpiration or entering groundwater or surface water. A piping network, often laid in a stone-filled trench (see weeping tile), distributes the wastewater throughout the field with multiple drainage holes in the network. The size of the drain field is proportional to the volume of wastewater and inversely proportional to the porosity of the drainage field. The entire septic system can operate by gravity alone or, where topographic considerations require, with inclusion of a lift pump. Certain septic tank designs include siphons or other devices to increase the volume and velocity of outflow to the drainage field. These help to fill the drainage pipe more evenly and extend the drainage field life by preventing premature clogging or bioclogging.