39° ENGINEERING ON THE FARM 



water used in the sinks and lavatories, and possibly some 

 heat is generated by chemical action in the tank itself. This 

 heat is conserved by having the tank partially or entirely 

 buried in the earth. Currents are prevented in the surface 

 of the sewage by baffles or partitions through the tank, the 

 sewage passing from one chamber to another through sub- 

 merged openings. The solid matter is thus decomposed 

 into liquids and gases, the gases passing off into the air, and 

 the liquid, which is free from dangerous germs, being either 

 discharged through a filter out upon the soil or carried away 

 by ordinary drains to an outlet ditch. This waste material 

 is thus deprived of its dangerous and unsanitary qualities 

 by a system that is simple and requires but little attention 

 after it has once been installed. Such systems, varying in 

 their detail to meet local conditions, are now in use in many 

 places throughout the country, and their operation is no 

 longer an experiment. 



Disposal of effluent. In the construction of a septic tank 

 it is necessary that some provision be made for the final 

 disposal of the liquid or effluent, for no liquid whatever is 

 destroyed in the tank; it must all flow away. Three different 

 methods of disposal have been used for the individual house 

 tank. The first and most simple method is the direct dis- 

 charge of the effluent from the tank into an ordinary farm 

 drain tile. A 4-inch tile should be used where the grade is 

 not less than i}4 inches to 100 feet. If less, a 5-inch tile 

 will make a satisfactory outlet. Tile drains which have 

 served as septic-tank outlets for five years or more, on flat 

 grades, show no filling or sedimentation due to their serving 

 as such an outlet. A drain of this nature carries the effluent 

 of the tank from the premises underground, and finally dis- 

 poses of it in some outlet ditch, where it is completely 

 removed by the storm waters after heavy rains. 



Open ditch. Where the liquid from a septic tank is carried 

 a short distance by the tile and discharged into a shallow 

 ditch, there is some trouble experienced in the wintertime 



