510 WATER SUPPLY AND SEWAGE DISPOSAL 



the decomposing and purifying action of bacteria. Sanitary 

 engineers, and students of sanitation generally, now agree that 

 the cesspool is an unsanitary method of disposing of sewage. 

 They are also agreed that one of the most feasible and sanitary 

 methods of disposing of sewage in case of isolated residences 



FIG. 315. Pollution of ground water: sewage discharging into sink-holes. 



is by using some type of SEPTIC TANK or DISPOSAL TANK and 



SUBSURFACE DRAINS. 



602. The Septic Tank. The modern SEPTIC TANK consists 

 of two, and often three, compartments (Figs. 316 and 317). 

 Each of these compartments is cemented so as to be absolutely 

 water-tight. The sewage from the house enters compartment 

 No. 1. In this compartment ANAEROBIC BACTERIA (Art. 465, 



