SANITATION' 393 



one-half gallon per foot, the number of tile needed in the 

 system can be determined from the size of the discharge 

 chamber in the tank. It is best to make the total contents 

 of the distributing system about 10 per cent larger than the 

 total contents of the discharging chamber. Where there 

 is a satisfactory outlet, or the fall is sufficient, a drain tile 

 laid about 30 inches deep around the distributing drains, 

 as shown in the figure, is very desirable, although not neces- 

 sary. Such a drain will prevent the soil from becoming 

 saturated at times of heavy rains. Where the absorption 

 method is used for disposal, it is necessary to have an 

 additional chamber in the tank for holding the liquid the 

 proper length of time. Such a chamber should be large 

 enough to hold all the liquid for approximately 24 hours, 

 and discharge it at the proper time in a short period. This 

 chamber must be fitted with a siphon or an automatic valve. 

 Such valves are carried in stock by dealers in plumbing 

 supplies and cost from $10 to $25 each. The discharge 

 from the septic chamber of the tank into the discharge 

 chamber should be carefully protected to prevent any 

 coarse material which will clog the valves and prevent 

 their operation from flowing through. The fact that these 

 valves often get out of order and cease to work is one of 

 the objections to this method of disposal, but, with care in 

 construction and by the use of a good valve, they will give 

 satisfactory results. 



Filtration method. The third method is by the use of a 

 filter attached to the discharge end of the tank and is not 

 considered practicable for the ordinary farmhouse. 



Form of septic tank. The form of septic tank is not mate- 

 rial, so long as the conditions favorable for septic action are 

 maintained. Light should be reduced to a minimum. A 

 small quantity of air passing through the outlet of the tank, 

 over the top of the liquid in the tank, and up through the 

 inlet and soil pipe of the house is beneficial rather than 

 detrimental. If the inlet or outlet of the tank is submerged 



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