178 



MARKET DAIRYING 



retain all sediment and floating material, since the dis- 

 charges permit the withdrawal of the liquid from near the 

 middle of the tank only. This is one of the main features 

 of the tank. All inorganic matter entering the tank will 

 gradually settle and, of course, remain in it. Some of 

 the organic matter tends to settle during the first 24 hours, 



after which it comes to the 

 surface to be gradually 

 wasted away by the action 

 of bacteria. This wasting 

 away is naturally very 

 slow, and since the slowly 

 gathering organic matter 

 nearly all remains in the 

 first section of the tank, 

 this must be large enough 

 to provide for a consider- 

 able accumulation of it. 



The tank should be built air tight, except in two places. 

 At the right is an air inlet, consisting of a goose-neck 

 pipe, which renders the vent at the top more effective. 

 This vent consists of a long shaft extending beyond the 

 top of the dairy, thus carrying off the foul gases caused 

 by the decomposition of the material within. One-inch 

 gas pipe, properly fastened, will serve as a satisfactory 

 vent. 



In order to afford communication of sections A and C 

 with the vent, the two partitions should not be built 

 quite as high as the tank. There should be at least one 

 inch space between the top of the partitions and the cover. 

 A iy'2-mch. gas- pipe should be laid over the tank 

 through which the water from the cooler and vats may 

 be discharged directly into the drain. This water 



Fig. 65. — Cross Section of Septic 

 Tank. 



