SANITARY DRAINAGE OF WASHINGTON. 13 



ever character that come to it, no halting by the way being possi- 

 ble. Incidentally to this, no matters should be admitted to the 

 sewer which its ordinary flow is not capable of removing. (2.) At 

 the head of each sewer, — technically called " the dead end," — 

 there should be placed a flush-tank, discharging, at least once in 

 twenty-four hours, a suflScient volume of water to sweep out all 

 material deposited higher up the stream than the point where the 

 efficient natural scouring begins, and to increase the depth of flow 

 throughout the lower portion of the line beyond that, at any time, 

 reached by the natural current, so that the matters adhering to the 

 walls of the sewer may be washed away. (3.) The material and 

 the jointing of the sewer should be such as to retain absolutely all 

 of the liquid portion of its contents ; the water of the sewage is 

 all needed as a vehicle for its heavier materials, and its escape into 

 the soil must produce the deleterious effect upon the " ground-air " 

 before referred to. 



The popular idea as to the size of drain required to receive the 

 outflow of a single house, or of a number of houses, is strangely in 

 error. A j^ipe 6 inches in diameter, having an inclination of 4 

 inches in 100 feet, has a capacity of discharge of nearly 200 gal- 

 lons per minute, — say 12,000 gallons per hour, or between 8 and 

 11 in the morning, 36,000 gallons. It is usual to estimate that 

 during these three hours about one-quarter of the daily flow is dis- 

 charged. Such a pipe then, at such an inclination, would be ade- 

 quate to the removal of nearly 150,000 gallons per day. If each 

 household averages six persons, and if the daily consumption of 

 water is even 50 gallons per head, the service would be sufficient 

 for 500 houses ; or, supposing the sewer to run only one-half full 

 during the hours of greatest use, for 250 houses. It is to be con- 

 sidered also that it is rarely necessary to lay a lateral sewer with so 

 slight a fall as four inches in 100 feet, and that an increase of fall 

 secures, of course, an increase of discharge. During the past year, 

 under the direction of the National Board of Health, I have made 

 a number of gaugings in different parts of the country to deter- 



