Vitrified salt-glazed clay or well-made concrete sewer pipe and cast-iron soil pipe are the standard materials for house sewers on farms. Asphalt-impregnated fiber pipe, of a type designed especially for house sewers, appears to be satisfactory for this purpose. Cast-iron soil pipe with leaded joints should be used when the sewer is within 50 feet of a well or suction line from a well, within 10 feet of any drinking-water supply line under pressure, within 5 feet of basement foundations, or when laid beneath driveways with less than 3 feet of earth covering the pipes. When within 15 feet of large trees or shrubs, the sewers should have root-tight joints.
Size
For house sewers, 4- and 6-inch pipes are generally used. Where a 4-inch pipe is used, cast-iron is commonly recommended. Grades with little fall require larger pipes. The large sizes are also less liable to become clogged. Clay pipe is made in pieces 2 or 21/2 feet long, whereas fiber-pipe sections are 4 feet long and cast-iron pipe 5 feet long, so that there are fewer joints. The minimum number of joints is desirable, as there is less danger of stoppage.
Alinement
Run the house sewer in a straight line and avoid bends whenever possible. Slight changes in direction may be made with one-sixteenth or one-eighth bend fittings. For sharper changes of direction a manhole or distribution box may be used. Changes in direction of more than 45 are not recommended unless a manhole is provided. Clean-outs are desirable within 5 feet of the septic tank where tanks are placed more than 20 feet from the building and the sewer line is not buried deeper than 4 feet.
Establishing Line and Grade
The trench for laying the sewer is usually dug after the septic-tank excavation has been completed and the elevation of the tank inlet determined. A simple method of setting guides for the excavation is illustrated in [figure 2].
Digging the Trench
Start digging the trench at the tank end, so that rain or seepage will have an outlet. Rounding the bottom of the trench to the shape of the pipe and hollowing out basins for the "bell" ends allows the pipe to rest firmly throughout its full length, permits full calking of joints, and relieves the strain on them.
Laying the Pipe