1. Water consumption of 40 gallons per person per day of 24 hours._Sewage and sewerage of farm homes [1922]

2. A detention period of about 24 hours; that is, the capacity of the

settling chamber below the flow line is approximately equal to the

quantity of sewage discharged from the house in 24 hours.

3. Where a siphon chamber is provided, its size is such that the dose of

sewage shall be approximately equal to 20 gallons per person; that is, the

capacity of the siphon chamber between the discharge and low-water lines

is roughly equal to the quantity of sewage discharged in 12 hours.

[Illustration: 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._

--------+--------+--------+--------------------------------------------

|Quantity| | Settling chamber.

| of |Capacity|

Number | sewage | below +-------+-------+-------+----+-------+---+---

of | in 24 | flow |Length.| Depth.|Width. | W. | X. | Y.| Z.

--------+--------+--------+-------+-------+-------+----+-------+---+---

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

--------+--------+--------+-------+-------+-------+----+-------+---+---

--------+----------+------------------------------------------------

| Quantity | Siphon chamber.

Number |of sewage +-------+--------+--------+----+----+----+-------

of | in 24 |Length.| Depth. | Width. | A. | B. | C. | D.

--------+----------+-------+--------+--------+----+----+----+-------

| Galls. |Ft. In.| Ft. In.| Ft. In.| In.| In.| In.| In.

5 | 180-280 | 5 0 | 2 8 | 2 0 | 3 | 4 | 15 | 18-1/4

10 | 320-480 | 8 0 | 2 8 | 2 6 | 3 | 4 | 15 | 20-1/4

15 | 520-680 | 8 8 | 2 10 | 3 0 | 4 | 4 | 17 | 20-1/4

20 | 720-960 |10 0 | 2 10 | 3 6 | 4 | 4 | 17 | 20-1/4

--------+----------+-------+--------+--------+----+----+----+-------

--------+---------+---------+--------+--------+---------+-------------

| of | | | | | in top slab

| | | | | +-------+------

--------+---------+---------+--------+--------+---------+-------+------

5 | 180-280 | 3 | 4-1/2 | 1-1/3 | 2-2/3 | 10 | 3

10 | 320-480 | 4-1/4 | 6-1/4 | 2 | 3-3/4 | 14 | 3

15 | 520-680 | 6-2/3 | 9-3/4 | 3 | 6 | 15-2/3| 4

20 | 720-960 | 8 | 12 | 3-1/2 | 7 | 17-1/2| 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.

[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.

Type 2

INCHES

+---+-------+-------+-------+-------+

Diameter of siphon | A | 3 | 3 | 4 | 4 |

Diameter of outlet | B | 4 | 4 | 4 | 4 |

Drawing depth | C | 13 | 15 | 14 | 17 |

Depth to floor | D | 16¼ | 18¼ | 17¼ | 20¼ |

Height above floor | E | 7¼ | 9¼ | 8¾ | 11¾ |

Clearance under bell | F | 2 | 2 | 2 | 2 |

to discharge line | G | 20½ | 22½ | 22¾ | 25¾ |

Discharge line, to top of wall | H | | | | |

Depth of outlet sump | I | | | | |

Length and width of outlet sump | J | | | | |

+---+-------+-------+-------+-------+

| R | 4 | 4 | 4 | 4 |

| S | 2 ft. | 2 ft. | 7 ft. | 8 ft. |

Diameter of carrier (R), and +---+-------+-------+-------+-------+

minimum fall (S) in feet | R | 5 | 5 | 5 | 5 |

per 100 feet | S | 1½ ft.| 1½ ft.| 2 ft.| 2½ ft.|

+---+-------+-------+-------+-------+

| R | 6 | 6 | 6 | 6 |

| S | 1 ft. | 1 ft. | 1 ft. | 1 ft. |

+---+-------+-------+-------+-------+

Type 3 Type 1

INCHES INCHES

+---+----+----+----+----+ +----+

Diameter of siphon | A | 3 | 3 | 4 | 4 | | 4 |

Diameter of outlet. | B | | | | | | |

Drawing depth | C | 13 | 15 | 14 | 17 | | 5 |

Depth to floor. | D | 17 | 17 | 19 | 22 | | 15 |

Height above floor | E | 13 | 13 | 15 | 18 | | 19 |

Clearance under bell. | F | | | | | | |

to discharge line. | G | 19 | 21 | 20 | 25 | | |

Discharge line, to top of wall. | H | 6 | 6 | 8 | 8 | | |

Depth of outlet sump | I | 13 | 13 | 11 | 12 | | |

Length and width of outlet sump | J | 18 | 19 | 19 | 18 | | |

+---+----+----+----+----+ +----+

]

The overhead siphon, type 3, figure 26, may be installed readily in a tank

already built by addition of an outlet sump. If properly set and handled,

sewage siphons require very little attention and flush with certainty.

Like all plumbing fixtures they are liable to stoppage if rags, newspaper,

and similar solids get into the sewage. If fouling of the sniffing hole

or vent prevents the entrance of sufficient air into the bell to lock the

siphon properly, allowing sewage to dribble through, the remedy is to

clean the siphon. Siphons are for handling liquid; sludge if allowed to

accumulate will choke them.

=Submerged outlet.=--The purpose of a submerged outlet is to take the

outflow from a point between the sludge at the bottom and the floating

solids or scum. The outlet in figure 25 may be readily made of sheet

metal by a tinsmith. Wrought iron or steel pipe with elbows or light

lead pipe may be used, the pipe being set in the concrete and left in

place. Sometimes a galvanized wire screen (1/4-inch mesh) is fitted over

the inner end to prevent large solids leaving the settling chamber and

possibly clogging the siphon or distribution tile. If a screen is used it

should be easily removable for cleaning.

[Illustration: Fig. 27.--Home-made reinforced concrete covers. (1) Slabs

placed crosswise permit uncovering the whole tank for cleaning, but as

inspection is somewhat difficult, cleaning is the more likely to be

neglected; (2) manhole, 18 inches square; cover, 22 by 22 by 3 inches

thick, easy to make and to slide or lift from the opening.]

=Manhole frame and cover.=--The frame and cover shown in figure 25 are

stock patterns made of cast iron and weighing about 250 pounds per set.

The cover is 21 inches in diameter; it is tight and, on account of its

weight, is unlikely to be disturbed by small children. The frame or rim

is about 7 inches high and 31 inches in longest diameter. If desired,

light cast-iron cistern or cesspool covers obtainable from plumbing supply

houses, home-made slabs of reinforced concrete (see fig. 27), or wooden

covers (see fig. 23) may be used.

=Overflow.=--The purpose of an overflow is to pass sewage to the

distribution field should the siphon stop working. The overflow (fig. 25)

is a 3-inch riser pipe with top 3 inches above the discharge line and the

bottom calked or cemented into the side outlet of a =T=-branch. The run of

the =T=-branch should correspond with the size of the sewer from the tank

to the distribution field. If this sewer is 4-inch pipe, a 4 by 3 inch

=T=-branch is used, the 4-inch spigot end of the siphon being calked or

cemented into the branch, as shown in figure 25; if the sewer is 5-inch,

a 5 by 3 inch =T=-branch is used and connected to the siphon with a 5-inch

to 4-inch reducer (in vitrified specials the equivalent is a 4-inch to

5-inch increaser); if the sewer is 6-inch, a 6 by 3 inch =T=-branch is used

and connected to the siphon with a 6-inch to 4-inch reducer.

=Concrete work.=--Before excavation for the tank is begun, two wooden

forms should be built for shaping the inside of the settling and siphon

chambers. In most instances the ground is fairly firm, so that the lines

of excavation may conform to the outside dimensions of the tank, the

back of the walls being built against the earth. The forms may be made

of square-edged boards, braced and lightly nailed, as shown in figure

28. The forms should have no bottom. If it is desired to lay the sides

and covering slab in one operation, the top of the forms must be boarded

over. All pipe and manhole openings should be accurately placed and cut.

The faces of the forms may be covered with paper or smeared with soap or

grease to facilitate removal later.

The ground should next be excavated to the proper depth for placing the

floors in both chambers. The settling chamber floor, being the lower,

should be placed first. Effort should be made to secure water-tight

work, a feature of especial importance where leakage might endanger a

well or spring. A concrete mixture of 1:2:4 is generally preferred (1

volume cement, 2 volumes sand, 4 volumes stone). The ingredients should

be of best quality and thoroughly mixed. The concrete should be poured

promptly and worked with a spade or flat shovel to make the face smooth

and eliminate pockets or voids within the mass.[10] Before the settling

chamber floor has hardened the form should be set upon the floor and the

concrete work continued up the sides. The pipe form for the submerged

outlet should be set. When the side walls of the settling chamber have

reached the bottom of the excavation for the siphon chamber, the siphon

trap with its connecting branch and short piece of pipe should be set to

proper line and grade and blocked in position. The floor of the siphon

chamber should now be poured and the form for that chamber placed thereon,

leaving a 6-inch or 8-inch space (according to the thickness of the

division wall) between the ends of the two forms. Pouring of all side

walls and the top slab should continue without stop, making the entire

structure a monolith.

[10] See footnote, p. 17. For more detailed information on form and

concrete work the reader is referred to U. S. Department of Agriculture

Farmers' Bulletin No. 481, "Concrete Construction on the Live-Stock

Farm."

[Illustration: Fig. 28.--Forms for concrete work--how to use them.

1. Make the forms as shown and to the dimensions required by fig. 25

and the table on p. 37; nails to be driven from the inside and left

projecting for drawing with a claw hammer.

2. Excavate to lines 6 or 8 inches, as may be required, outside of the

forms and to the depths required for both chambers.