346 MARKET DAIRYVING 
requires no purification and, if conducted through the 
tank, would necessitate one of too large dimensions. 
Moreover, the large amount of cold water needed for 
cooling milk and cream would cool the contents of the 
tank too much for a rapid decomposition of the material 
within. 
Size of Tank. This must necessarily depend upon the 
amount of sewage run into it. In general it should have 
capacity sufficient to hold all of one day’s waste in the 
smallest section (C). It will be noticed from the cut 
that section A is considerably larger than either of the 
other two. The reason for this is that nearly all of the 
inorganic matter remains in the bottom of this part of the 
tank, while the organic matter, as already stated, gradu- 
ally accumulates at the surface in this section, in spite 
of constant decomposition. Where the tank receives the 
sewage from both the dairy and the dwelling, a tank 
12 feet square by 414 feet deep will be large enough, 
provided the water used for cooling is not run into it. 
It is well to remember, however, that the larger the tank 
used the better the results that may be expected from it. 
Flow of Sewage Through Tank. Four-inch tile, 
carefully laid, may be used to conduct the sewage from 
the dairy to the tank. A trap is placed near the dairy 
to shut off the odors coming from the drain. At the 
point at which the sewage enters the tank it is desirable 
to attach an elbow with an arm sufficiently long to keep 
the lower end always in the sewage. This prevents un- 
due mixing of the incoming sewage with that already 
in the tank, a matter of importance in the successful 
operation of the tank. 
When the sewage in section A has reached the dotted 
line, it begins to discharge into section B through three- 
