The 4-inch siphon has a drawing depth of 33 inches, and as the siphon chamber is 4 feet wide by 6 feet long the dose is about 500 gallons. The siphon cost $35. The 6-inch sewer to the switch box falls about 6 inches in 50 feet. The distribution field was thoroughly subsoiled, and about 800 feet of 3-inch tile was laid in each unit. At intervals of 25 feet along the distribution trenches 6-inch holes were dug through the clay stratum with a posthole digger. These holes were filled with stone and constitute the filter wells previously mentioned. All tile lines are surrounded with stone and coarse gravel, and the ground has been trimmed to give a uniform cover of 12 inches. All work was done by day labor in a thorough manner. As the men were doing other work at the same time the actual cost is not known, but it is believed the installation cost about $700.
Cost data.—Reliable cost figures are difficult to estimate. Labor, materials, freight, haulage, and other items vary greatly in different localities. The septic tank shown in [figure 23] contains about 1,000 bricks and is estimated to cost $60 complete. The septic tank shown in [figure 25] for 5 persons is estimated to cost $135; for 10 persons, $170; for 15 persons, $240; for 20 persons, $280. In Maryland, in 1916, the cost of installing a septic tank similar to that shown in [figure 25] (for 5 people), including 86 feet of 5-inch house sewer (55 feet of cast-iron pipe passing a well, and 31 feet of vitrified pipe) and 214 feet of second-quality 4-inch sewer pipe in the distribution area, was as follows:
| Excavation, labor | $7.50 |
| Materials delivered | 46.60 |
| Three-inch siphon, including freight | 15.75 |
| Construction, labor | 28.00 |
| Supervision | 5.00 |
| Total | 102.85 |
The quotations in the following table will be found useful in making estimates of cost:
Cost of pipe and drain tile.
(February, 1921.)
| Kind of pipe. | Size, in inches. | ||||
| 3 | 4 | 5 | 6 | ||
Extra heavy cast-iron soil pipe, on cars Chicago, Ill., | per foot | $0.34 | $0.46 | $0.61 | $0.72 |
Vitrified salt-glazed sewer pipe, on cars Chicago, Ill. | do | .15 | .15 | .22½ | .22½ |
Vitrified salt-glazed sewer pipe, at factory near | do | .12 | .12 | .18 | .18 |
Clay or shale drain tile, at factory in Ohio | do | .03 | .03½ | .04½ | .05½ |
Clay or shale drain tile, at factory near Washington, D. C. | do | .04 | .05 | .06 | .07 |
The cost of cast-iron fittings may be roughly estimated as follows: Bends, one to one and one-half times the price of straight pipe; T-branches, two times the price of straight pipe; reducers, average of the prices of straight pipe at each end. The cost of clay bends, T-branches, reducers, and increasers may be roughly estimated at four times the price of straight pipe.
Operation.—Attention must be given to every plant to insure success. Unusual or excessive foulness should be investigated. No chemicals should be used in a septic tank; garbage, rags, newspaper, and other solids not readily soluble in water should be kept out of sewers and tanks. The plant should be inspected often, noting particularly if the siphon is operating satisfactorily. If scum forms in the settling chamber it should be removed, and the sludge should be bailed or pumped out yearly. Frequently tanks are not cleaned out for three or four years, resulting in large quantities of solid matter going through to the distribution system and clogging it. Clogging may occur in the tile or in the adjacent soil. In either case the tile should be dug up, cleaned, and relaid. In some cases it has been found advantageous to relay the tile between the former lines. When sewage is applied to fairly porous land at the slow rate here recommended and the plant is well handled the tile lines should operate satisfactorily for many years. Liming heavy soils tends to loosen and keep them sweet.