Septic-tank systems, if installed and maintained properly, provide the
most sanitary method of sewage disposal for farmhouses equipped with
running water.
Ground water or rock close to the surface, lack of sufficient fall for
the sewage to flow by gravity, and too small an absorption area for the
effluent limit the satisfactory operation of a septic tank. When these
conditions exist, special advice should be sought from a competent
local sanitary authority. Adverse soil conditions can be overcome if
sufficient fall and space are available.
The five essential parts (fig. 1) of a septic-tank system are (1)
the house sewer; (2) the septic tank; (3) the effluent sewer; (4)
the distribution box; and (5) the disposal field. In special cases a
grease trap (see fig. 11, p. 19) is added. To facilitate inspection and
repairs it is good practice to keep in the house a chart showing the
location of the tank and other parts of the system.
A septic tank does not necessarily purify the sewage, eliminate odor,
or destroy all solid matter. Its purpose is to condition the sewage or
domestic waste by bacterial action, so that it can be disposed of in a
more satisfactory manner.
[Illustration: Figure 1.--A septic-tank system.]