[Illustration: Fig. 24.--Two-chamber septic tank, simple and inexpensive. Constructed of 24-inch vitrified sewer pipe; size suitable for 125 gallons of sewage daily (nominally 3 persons). _A_, House sewer; _B_, settling chamber, made of one double =T= branch and one length of straight pipe, each 3 feet long and 2 feet in diameter, supported by 4 inches of concrete, all joints made water-tight; _C_, submerged outlet, consisting of a metal =T= slipped into the sewer-pipe branch; _D_, wire screen, 2-inch mesh; _E_, siphon chamber made of one =T= branch 3 feet long and 2 feet in diameter; _F_, siphon; _G_, 3-inch overflow; _H_, sewer to distribution field; _I_, tight cover with lifting ring; _J_, concrete protection around sewer-pipe hubs.] [Illustration: Fig. 25.--Typical two-chamber concrete septic tank. (See table for dimensions and quantities for different sizes.)] Three types of sewage siphon are shown in figure 26. In all, the essential principle is the same: A column of air is entrapped between two columns of water; when the water in the chamber rises to a predetermined height, called the discharge line, the pressure forces out the confined air, destroying the balance and causing a rush of water through the siphon to the sewer. The entire operation is automatic and very simple. The siphons shown are commercial products made of cast iron; they have few parts and none that move, and the whole construction is simple and durable. The table (fig. 26) lists stock sizes adapted to farm use. Manufacturers furnish full information for setting their siphons and putting them in operation. For example, take type 2, figure 26: (1) Set siphon trap (=U=-shaped pipe) plumb, making E (height from floor to top of long leg) as specified; (2) fill siphon trap with water till it begins to run out at B; (3) place bell in position on top of long leg, and the siphon is ready for service. Do not fill vent pipe on side of bell. [Illustration: Fig. 26.--Three types of sewage siphon. The table gives dimensions for setting standard 3 and 4 inch siphons; also the appropriate size and grade of the sewer to carry the siphon discharge.] [Transcriber Note: The data for Type 1 Siphon has been added to the table.