Drain Fields, or soil absorption areas, come in all shapes and sizes, depending on the age of the home and the lay of the land.
There are, however, two general types of facilities to carry off the overflow water from the septic tank:
Trench systems and drainage pits.
Trench systems - also called leaching fields, drain fields, or finger systems - generally consist of a network of perforated pipes laid in a gravel-lined trench. Solids clogging pipe perforations, gravel lining, or the soil pores outside the trench will cause drainage to slow or eventually stop.
Drainage pits - also called drywalls or cesspools - are made of precast concrete or concrete block. They are cyclinders with closed tops, open bottoms, and holes in the sidewalls. Some older systems consist of only a drainage pit or cesspool.
Solids accumulating on the interior surfaces of the pit or in the soil will again contribute to sluggish drainage or failure.