DAIRY AND FARM SEWAGE 137 



is in a liquid or semi-liquid state. At this point the sewage is 

 practically deprived of any disagreeable odor, and that which is 

 still retained is not objectionable. To prove the efficiency of this 

 method of purification, sewage after passing through the tank, 

 being thoroughly decomposed, can be kept for weeks at a very 

 favorable temperature, showing no signs of the development of 

 putrefactive odors. It should require from three to four days, 

 however, for sewage to pass through this tank to thoroughly de- 

 odorize it. Three partitions in a tank, as described above, have 

 proven very efficient. However, a tank with two compartments is 

 very satisfactory, but in no case can a tank without compartments 

 be recommended. 



LOCATION OF SEPTIC TANK 



There should be a slight fall from the stable to the septic tank, 

 and from this tank to the irrigating system. A septic tank can 

 be located as far as convenient, or as near as desirable, to the 

 traps. This is a matter that depends upon conditions entirely. 

 However, in all cases the inlet and outlet drains of the system, as 

 far as the point of irrigation, should consist of sewer pipe with 

 joints cemented. A preferable location for the tank is about a 

 foot to eighteen inches in the ground. This prevents freezing, 

 which checks decomposition. However, there are instances in 

 which the slope of the ground from the stable to the irrigated 

 field is so slight that the septic tank needs to be put above the 

 ground. In that case it is advisable to cover the tank with earth, 

 straw, or barn-yard manure, to prevent freezing. 



PRECAUTIONS 



Care should be taken that no strong disinfectant, such as cor- 

 rosive sublimate, is allowed to be run into the septic tank from 

 the stables or house, since any disinfectant prevents the action of 

 the bacteria in the tank; consequently a large part of the sewage 

 will remain in a solid form and the tank will soon fill up. 



CLEANING OUT THE TANK 



The frequency of cleaning this tank depends entirely upon the 

 kind of sewage discharged into the tank. All organic matter is 

 readily decomposed and will flow through the tank, as has been 

 stated before, but inorganic matter, such as sand, crushed rock, 

 cinders, etc., cannot be decomposed and will remain in the same. 

 If due precaution is taken in not allowing too much of this inor- 

 ganic matter to flow into the tank, there is little need of cleaning 

 it. For a cow barn such a tank need not be cleaned oftener than 

 once in eight months. The tank at the College has not been 



