SEWAGE DISPOSAL 115 



soil would soon become clogged with the undecomposed or- 

 ganic matter. The tiles should he laid near the surface of 

 the soil, so that oxygen shall be available for the aerobic 

 bacteria. 



The tile may be laid in ciiuh-rs or gravel if the soil is 

 heavy in character. A sandy soil is best adapted for such 



Fig. 23. The Tile Drain of a Sewage Purification System 



The tile are laid near the surface of the ground and surrounded with coarse 



material like gravel or cinders in order that the sewage may pass freely out 



of the drains into the ground in which the final steps in its decomposition 



take place. These processes require an abundance of oxygen 



a disposal system, but the method can be used in most 

 types of soil. Since but little solid matter other than or- 

 ganic enters the septic tank, the accumulation of sludge is 

 slow, and the tank will not have to be cleaned for several 

 years. The drains may have to be dug up and the tiles 

 cleaned once in three or four years, as earthworms bring in 

 a good deal of soil. The system will work with little atten- 

 tion, and furnishes a means by which the farm home can 

 dispose of the household sewage in a convenient and harm- 



