A septic tank is used to detain domestic wastes to allow the settling of solids prior to distribution to a Leach field for soil absorption. Septic tanks are used when a sewer line is not available to carry them to a treatment plant. A settling tank in which settled sludge is in immediate contact with sewage flowing through the tank, and wherein solids are decomposed by anaerobic bacterial action.

-See also:
"septic tank" is in the NAICS Code "562998"
All Other Miscellaneous Waste management Services
... operation of materials recovery facilities, septic tank pumping and related services, and waste mana ...