THE SEPTIC TANK 153 



tion. In homes where no proper provision is made, we 

 frequently find sewage running into open drains, or even 

 upon the soil, there becoming a dangerous menace to 

 health. Most country homes nowadays have a cesspool. 

 This is nothing more or less than a deep hole dug in the 

 earth, having an open bottom, uncemented rock or brick 

 walls and a covered top. It is situated a few feet away 

 from the house, and receives all the sewage which drains 

 out gradually through holes at the sides and bottom into 

 the surrounding soil. If a great deal of water is used, the 

 cesspool is too small, and satisfactory drainage is impos- 

 sible. Moreover, unless great care is taken, there is dan- 

 ger of drainage into a near-by well. In clayey soils, cess- 

 pools give much trouble, as little drainage takes place, and 

 frequent pumping out is necessary. A cesspool should be 

 simply a temporary means of getting rid of sewage. 



The septic tank. By far the most modern and hygienic 

 method of sewage disposal is by means of what is known 

 as the septic tank. It has been discovered that? there are 

 two types of bacteria, one of which (anaerobic) thrives 

 without air, releasing oxygen from the substances on which 

 it feeds, and another (aerobic) that must have air. The 

 septic tank is made with at least two compartments, both of 

 which are made of cement and are water-tight. In the first 

 compartment sewage from the house flows, and is there 

 attacked by the anaerobic bacteria, which cause the solid 

 matter to become liquid. Fats and other substances rise 

 to the surface, forming an almost air-tight scum, which 

 assists the anaerobic bacteria to do their work more effec- 

 tively. As the sewage is decomposed it passes into the 

 second tank in an almost colorless and odorless condition. 

 When this tank fills its contents are siphoned off into 



