Septic Metrics

Septic system diagram with every part explained

Updated . Based on the sources listed below. Expert review pending.

Short answer

A conventional septic system has four main stages. A pipe carries wastewater from the house to a buried tank. The tank separates solids from liquid. Liquid then flows, often through a distribution box, to a leach field. There, pipes or chambers release it into the soil for final treatment.

Both drawings below show a conventional gravity system. Treat them as a general picture: your own layout may differ, and your permit record is the place to find where things really sit on your property.

Side view

This cut-away follows the water from the house down into the soil.

Cut-away diagram of a conventional septic system Wastewater runs from a house through a buried pipe into a septic tank with layers of scum, liquid and sludge. Liquid leaves through an outlet to a distribution box, then along a perforated pipe in a gravel trench, and soaks down into the soil. HouseSeptic tankDistribution boxLeach fieldSoilScumLiquidSludge 12345

Top view of a typical yard

From above, under the lawn, the same system might look like this. According to the University of Georgia, the tank is often 10 to 20 feet from the house, in line with the sewer pipe.

Top view of a conventional septic system in a yard From left to right: a house, a sewer pipe, a rectangular septic tank with two lids, a pipe to a distribution box, and four parallel leach lines in the lawn. A dashed area beyond them is marked as a possible reserve area. House Reserve area, if any Septic tank Lids Box Pipe Leach lines
Simplified and not to scale. Real layouts vary, so check your permit record.

What does each part do?

PartWhat it does
Building sewerThe main pipe carrying all wastewater out of the house
Septic tankHolds wastewater so that solids sink as sludge and fats float as scum
Baffles or teesSlow incoming water and keep scum and solids from leaving
Lid or riserGives access to the tank for pumping and inspection
Effluent filterOn some tanks, catches small solids at the outlet
Distribution boxOn many systems, divides the flow between leach lines
Leach fieldPipes or chambers that release liquid into the soil
SoilRemoves harmful bacteria, viruses and nutrients

How do other system types differ?

The tank stage looks much the same on most systems. It's what happens after the tank that changes:

  • Mound systems add a pump chamber and build the field in a raised sand mound, for shallow soil or high groundwater.
  • Aerobic systems add oxygen to a treatment tank, and some finish with a tank that disinfects.
  • Drip systems add a dose tank and timed pumping to feed tubing near the surface.
  • Chamber systems swap the gravel for connected plastic chambers.

Want the step-by-step version? Read how a septic system works.

Rules vary by location

Your county may hold a drawing of your own system. Ask your local health department for the permit file.

Sources