Figure 6.—Method of outlining a septic-tank excavation on the ground surface.
Figure 7 shows how an inside form can be built and hung in place. The inlet and outlet tees should be carefully set and tied in place before the concrete is poured. A single length of pipe should be joined to the tee, so that the two can be set in the form as one unit. In most cases the earth walls of the excavations will serve as the outside forms unless the soil is sandy or gravelly and the excavation is deeper than 5 feet. If outside forms are used, space must also be provided for them. Forms should be constructed before the excavation is made and the tank built as soon as practical, to avoid warping of forms and caving of earth walls.
Figure 7.—Inside form hung in place for single-chamber septic tank, also a form for casting concrete-slab cover in sections.
County agricultural agents, local health departments, building-material dealers, and other agencies often have forms that may be borrowed or rented.
The effluent sewer should be constructed in similar manner and of the same materials as the house sewer and on a slope of 1/8 inch to 1 foot. This line, however, may be laid of terra-cotta pipe, as cast-iron is not considered necessary except in unusual cases. This line should always terminate in a distribution box from which the tile lines of the disposal field lead away. For steep slopes the arrangement shown in [figure 9] ([p. 15]) is practical. Joints must be of root-tight construction if the sewer is in the vicinity of trees or shrubs. The length of the sewer depends upon the distance from the tank to a safe site for the disposal field.