394 



ENGINEERING ON THE FARM 



so that there cannot be a free passage of air, a small air vent 

 should be left in the top of the tank. Figure 305 shows the 

 general arrangement of the outlet and inlet with the house 

 and soil pipe. The tank must be sufficiently protected from 



>4 



3 



After University of Minnesota 



Fig. 305. General arrangement of tile drain, septic tank, foundation 



of house, and soil pipe through house. Air circulation 



is indicated by arrow. 



the weather to prevent the temperature from going below 

 50 or 6o° Fahrenheit. In Minnesota it has been found that 

 2 feet of earth over the top of the tank is ample protection 

 for the winter months. 



It is very important that the inlet and outlet be so arranged 

 that there can be no movement on the surface of the liquids, 

 for the bacterial action takes place in the scum which accu- 

 mulates and floats on the surface. If currents of water strike 

 this, the scum is broken and a movement caused which pre- 

 vents the proper bacterial action. The flow of sewage 

 through the tank must be regulated by partitions or baffles. 

 These can be made of any material or in any style desired, 

 so long as they accomplish the purpose of breaking up all 

 horizontal motion on the surface of the liquid. 



