USE OF FLUSH-TANKS 239 



that an 8-inch pipe on a 0.4 per cent grade will flow one-third 

 full at a distance of 300 to 400 feet from the tank discharging 

 the above amount; and that on a 5 per cent grade the water 

 will come down as a solid piston for any dischrage greater than 

 14 cubic feet. 



The manager of the Pacific Flush- tank Company writes 

 that as a rule he does not interfere with engineers in their design 

 for tanks, but, in his opinion, a flush of 175 gallons on a i per 

 cent grade is sufficient, and on any flatter grade twice that 

 amount of water should be used, or, as he says, " long lines or 

 flat grades require greater capacity of tanks than steep grades 

 or short lines." 



Conclusions. The following conclusions are based upon 

 previously published data on this subject; upon the experi- 

 ence of engineers in different parts of the country; upon the 

 flushing diagrams recently published by J. W. Adams, and upon 

 observation and the special experiments made in Ithaca; and 

 it is believed that they are justifiable and a safe guide in the 

 use of flush-tanks. 



(1) Flushing of some sort is required at the upper ends 

 of laterals, the frequency and amount depending on the num- 

 ber of house-connections, on the carefulness or prodigality in 

 the use of water by the house-holders, on the grade and size 

 of the sewer, on the character of its construction, and on a 

 mysterious something which defies definition, but which pro- 

 duces frequent accumulations in one line and does not affect 

 another, apparently like the first. 



(2) This variety in the conditions prevents any exact state- 

 ment of a relation between the quantity of water which should 

 be discharged from a flush-tank and the grade of a sewer, but 

 it plainly indicates that the advantage of automatic flush- 

 tanks lies in a general guarantee or insurance against accumula- 

 tions in the upper part of the laterals, while periodic hand-flush- 

 ing must be depended on only when in charge of a responsible, 

 indefatigable, and intelligent caretaker. 



(3) Judging by the experience at Ithaca, and despite the 



