The outlet pipe must be provided with a vent (g) to prevent the tank 

 from being emptied by the siphon (e and f). 



The drain should be ordinary soft porous drain tile laid end to end 

 with loose open joints. The ditch in which the tile are laid should be 

 about four feet deep. Before the tile are laid, one foot of loose gravel 

 should be placed in the ditch and one foot of loose gravel on top of the 

 tile, and the ditch then filled with dirt. If this line of tile is four or five 

 rods long, it will never become clogged unless the soil is a very compact 

 clay. If the soil is of such a nature, two lines should be laid from the 

 "V"-shaped junction, having, as shown at H, gate valves so that the 

 flow can be alternated every two weeks, giving each line time to dry out. 



Size 



For a family of ten or twelve people, a tank six feet long, four feet 

 wide and four feet deep, holding 718 gallons, will be large enough. Such 

 a tank should take care of a sink, laundry, bath and toilet room, and the 

 overflow from a cistern. The receiving chamber should be about four 

 feet by two or three feet, and as deep as the main tank. After the tank 

 has been in operation a year or two, if any great amount of sludge has 

 accumulated on the bottom, it should be pumped out. If the tank is 

 properly constructed, the accumulation is very little, even after it has 

 been in operation several years. 



Caution 



Care must be taken not to empty into the intake pipe potato peelings 

 and other coarse substances that will not pass through a trap freely. 



Chloride of lime interferes with the bacterial action; hence, it should 

 not be used to any great extent in the sink. 



Bacteria do not materially change grease. If it enters the tank sys- 

 tem in great quantities, it eventually clogs it. It is often necessary to 

 have a grease trap below the sink. 



To prevent gases from escaping, the manhole covers should be made 

 tight by using cement or asphalt. 



A system of this kind will not freeze in winter, as the gases arising 

 from the sewage in the tank generate enough heat to counteract cold and 

 prevent freezing. 



The secret, if secret it may be called, of the whole system is the dark 

 air-tight tank, the submerged inlet and submerged outlet. The bac- 

 teria will do their work if not disturbed, but if the scum is molested, the 

 bacterial action does not take place. 



