Nearly 20 million homes, which include almost 30% of the population of the United States, dispose of their waste-water through an on-site disposal system. The most commonly used type of system is the septic tank, which is an individual treatment system that uses the soil to treat small wastewater flows. The system is usually used in rural or large lot settings where centralized wastewater treatment is impractical. Septic tank systems are designed specifically for each site, using standardized design principles that are usually state-regulated. Septic tank systems commonly contain three components: the septic tank, a distribution box, and a drainfield, all of which are connected by conveyance lines.

The septic tank serves to separate solids from the liquids in the wastewater. All sources of wastewater, including those from sinks, baths, showers, washing machines, dishwashers, and toilets, are directed into the septic tank, since any of these waters can...