There are three main types of systems to carry off the overflow water from the septic tank: leaching fields, filter beds, and drainage pits (also called dry wells or cesspools).
These generally consist of a network of perforated pipes laid in a gravel-lined trench. Solids clogging the pipe perforations and areas around the gravel will cause drainage to slow and eventually stop.
Filter beds work on the same principle as leaching fields, with a perforated pipe running through layers of sand and crushed stone. Filter beds are wider than leaching fields, and can be constructed above or below ground. They are smaller than leaching fields and can be utilized where property is not large enough for the long trenches required for a leaching field. Solids clogging the perforated pipe or the sand will cause drainage to slow and eventually stop.
Drainage pits are pre-cast or concrete block cylinders. They have closed tops, open bottoms, and holes in the sidewalls. Some older septic systems consist of only a drainage pit or cesspool.