A septic tank naturally produces gases (caused by bacteria breaking down the organic material in the wastewater), and these gases don't smell good. Sinks therefore have loops of pipe called P-traps that hold water in the lower loop and block the gases from flowing back into the house. The gases flow up a vent pipe instead -- if you look at the roof of any house, you will see one or more vent pipes poking through.
As new water enters the tank, it displaces the water that's already there. This water flows out of the septic tank and into a drain field. A drain field is made of perforated pipes buried in trenches filled with gravel. The following diagram shows an overhead view of a house, septic tank, distribution box and drain field:
A typical drain field pipe is 4 inches (10 centimeters) in diameter and is buried in a trench that is 4 to 6 feet (about 1.5 m) deep and 2 feet (0.6 m) wide. The gravel fills the bottom 2 to 3 feet of the trench and dirt covers the gravel.
The water is slowly absorbed and filtered by the ground in the drain field. The size of the drain field is determined by how well the ground absorbs water. In places where the ground is hard clay that absorbs water very slowly, the drain field has to be much bigger.
A septic system is normally powered by nothing but gravity. Water flows down from the house to the tank, and down from the tank to the drain field. It is a completely passive system.
You may have heard the expression, "The grass is always greener over the septic tank." Actually, it's the drain field, and the grass really is greener -- it takes advantage of the moisture and nutrients in the drain field.
Free Septic evaluations
Septic tank pumping
Septic Lid and Riser replacements
High pressure line jetting
Septic tank installations
Septic enzyme treatment
Drain Field Installations
Lift station maintenance
Real estate inspections
City sewer tie in
Grease trap pumping
Grease F.O.G. Manifests
Sewer permitsSink and toilet drains
Shower drains and floor drains
Sewer drain cleaning and high-pressure water jetting