How a Septic System Works: Tank, Effluent and Drainfield
A plain-English explanation of how conventional septic systems separate solids and treat wastewater onsite.
A conventional septic system treats household wastewater onsite instead of sending it to a municipal sewer. The tank and drainfield perform different jobs.
Wastewater enters the tank
Flow slows so heavier solids can settle as sludge and lighter material can form a scum layer.
Effluent leaves the tank
Liquid from the clearer middle zone moves through the outlet toward the drainfield. Baffles or tees help retain solids.
Soil does important treatment
The drainfield distributes effluent into unsaturated soil, where physical, chemical and biological processes provide further treatment.
Pumping protects downstream treatment
Removing accumulated tank solids reduces the chance they migrate into the drainfield.