Time honored method for sewage effluent disposal.  Still preferred by some today due to it's simplicity, economy, and reliability.  A pipe and stone bed is installed in the ground, usually finished off flush with the existing ground level.  Piping is 4" perforated PVC with 2 rows of holes, 1 set at 5 o'clock, the other at 7 o'clock, the pipe laid level.   Perforated piping is fed by a distribution box.   The distribution box has equalizers to help regulate the flow even if the d-box settles out of level.  Flow to all the lines should be as equal as possible.  Configuations can be absorption trenches, up to 48" wide or  absorption beds wider than 48" with multiple distribution piping runs to disperse effluent equally.  Effluent may run to the bed or trench by gravity or be pumped to the d-box.  In ground dispersal areas such as these require relatively good soils conditions and cannot be used where ledge or hard pan soils are near the surface, as a rule.