DISPOSAL OF SEWAGE 



513 



SUBSURFACE DRAINS (Fig. 318). Compartment 3 is sometimes 

 omitted and the siphon is placed in compartment 2, the dosing 

 tank, where it is submerged by the liquid. It is more con- 

 venient, however, to set the siphon in a separate compartment, 

 since it is necessary occasionally to examine the siphon to see 

 that it is working properly. 



603. The Imhoff Septic Tank. A septic tank of somewhat 

 more expensive construction is now generally used in disposing 



Fio. 319. Imhoff type of tank and sand filter for small institutions. 

 (Indianapolis Country Club.) (Courtesy of Chas. Brossman.) 



of sewage from cities and institutions where considerable quan- 

 tities must be taken care of. In the IMHOFF TYPE, the septic 

 tank is really composed of two compartments, one suspended 

 within the other (Figs. 319 and 320). The inner, suspended 

 compartment is the SETTLING CHAMBER; the lower compart- 

 ment is the SLUDGE CHAMBER. The two sides of the settling 

 chamber do not quite meet at the bottom (Sec. AA, Fig. 

 319) . As the sewage passes through this settling chamber, the 



33 



