344 MARKET DAIRYING 
both the dairy and the dwelling is to run it into a septic 
tank (see Fig. 73, designed by the author) and from 
this into a net-work of tile laid underground where it 
will irrigate and fertilize the soil. 
Object of Septic Tank. The main purpose of the 
tank, as its name indicates, is to thoroughly decompose 
all organic matter entering it. This is accomplished by 
numerous species of bacteria, and the tank may be 
properly designated as a germ incubator. Where the 
VENT 
Pree BSS LINE 
BUNS INE: | 
VYASTEWATER FROM | CoorerR ET 
a) ? 
MANHOLE NN 
SSS > w 
a er sees 
I | 
NOE) eo 
AiR INLET 
Discwar@ 
DischarRGe 
v 
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1 
om. 
f 
DISCHARGE 
Fig. 73.—Septic Tank. 
sewage is emptied into underground tile, the tank also 
serves as a storage, discharging its contents intermittently. 
This is necessary to force the liquid to all points of the 
system and to allow time for each discharge to soak away 
before the appearance of the next. 
Construction of Tank. Tlie general plan of construc- 
tion is illustrated in Figs. 73 and 74. The tank is located 
in the ground with the top within a foot or two of the 
surface. For durability it is preferably constructed of 
brick, stone or concrete. The tank is so constructed as to 
