Sewage and sewerage of farm homes [1922]

by George M. Warren

Fig. 23.—One-chamber septic tank—does nothing more than a tight cesspool. Brick construction, heavily plastered inside; size suitable for 180 to 280 gallons of sewage daily (nominally 4 to 7 persons).

A simple one-chamber brick tank suitable for a household discharging 180 to 280 gallons of sewage daily is shown in [figure 23]. A small two-chamber tank constructed of 24-inch vitrified pipe, suitable for a household discharging about 125 gallons of sewage daily, is shown in [figure 24]. A typical two-chamber concrete tank is shown in [figure 25]. Excepting the submerged outlet, all pipes within the tank and built into the masonry are cast-iron soil pipe with cast-iron fittings. Vitrified or concrete sewer pipe and specials are generally used as they are frequently more readily obtainable and a slight saving in first cost may be effected. Cast iron is less liable to be broken in handling or after being set rigidly in masonry, and the joints are more easily made water-tight. The submerged outlet is midway of the depth of liquid in the settling chamber. The inside depth of the siphon chamber is the drawing depth of the siphon plus 1 foot 5 inches.

The following table gives the principal dimensions with quantities of materials for four sizes of tank as illustrated in [figure 25]:

Dimensions and quantities for septic tanks.

Number of persons.	Quantity of sewage in 24 hours.	Settling chamber.
		Capacity below flow line.	Length.		Depth.		Width.		W.	X.		Y.	Z.
	Galls.	Galls.	Ft.	In.	Ft.	In.	Ft.	In.	In.	Ft.	In.	In.	In.
5	180-280	240	4	0	5	0	2	0	6	2	0	4	6
10	320-480	420	5	0	5	6	2	6	6	2	3	4	6
15	520-680	620	5	6	6	0	3	0	8	2	6	5	8
20	720-960	860	6	0	6	6	3	6	8	2	9	5	8

Number of persons.	Quantity of sewage in 24 hours.	Siphon chamber.										Concrete.	Cement.	Sand.	Stone.	Reinforcement in top slab (strip of heavy stock fencing).
		Length.		Depth.		Width.		A.	B.	C.	D.					Length.	Width.
	Galls.	Ft.	In.	Ft.	In.	Ft.	In.	In.	In.	In.	In.	Cu. Yd.	Bbls.	Cu. Yd.	Cu. Yd.	Ft.	In.
5	180-280	5	0	2	8	2	0	3	4	15	18¼	3	4½	1⅓	2⅔	10	3
10	320-480	8	0	2	8	2	6	3	4	15	20¼	4¼	6¼	2	3¾	14	3
15	520-680	8	8	2	10	3	0	4	4	17	20¼	6⅔	9¾	3	6	15⅔	4
20	720-960	10	0	2	10	3	6	4	4	17	20¼	8	12	3½	7	17½	5

Siphons.—Reference has already been made to the vital importance of air in sewage filtration. If the spaces within a filter or soil are constantly filled with water, air is excluded, and the action of the filtering material is merely that of a mechanical strainer with its clogging tendency. The purpose of a siphon is twofold: (1) To secure intermittent discharge, thus allowing a considerable period of time for one dose to work off in the soil and for air to enter the soil spaces before another flush is received; (2) to secure distribution over a larger area and in a more even manner than where the sewage is allowed to dribble and produce the conditions of the old-fashioned sink drain—namely, a small area of water-logged ground.

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.