The next step in evolution is the sanitary privy. Its construction must
be such that it is practically impossible for filth or germs to be spread
above ground, to escape by percolation underground, or to be accessible to
flies, vermin, chickens, or animals. Furthermore, it must be cared for in
a cleanly manner, else it ceases to be sanitary. To secure these desirable
ends sanitarians have devised numerous types of tight-receptacle privy.
Considering the small cost and the proved value of some of these types, it
is to be regretted that few are seen on American farms.
The container for a sanitary privy may be small--for example, a
galvanized-iron pail or garbage can, to be removed from time to time by
hand; it may be large, as a barrel or a metal tank mounted for moving;
or it may be a stationary underground metal tank or masonry vault. The
essential requirement in the receptacle is permanent water-tightness to
prevent pollution of soils and wells. Wooden pails or boxes, which warp
and leak, should not be used. Where a vault is used it should be shallow
to facilitate emptying and cleaning. Moreover, if the receptacle should
leak it is better that the escape of liquid should be in the top soil,
where air and bacterial life are most abundant.
Sanitary privies are classified according to the method used in treating
the excretions, as dry earth, chemical, liquefying.