[5] For information on making and placing concrete, see Farmers'
Bulletin 1772, Use of Concrete on the Farm.
A convenient method of assuring correct location of the tank is to
build a frame as shown in figure 6. Care is necessary to aline it with
the center line of the inlet and outlet and to level it so that the
distance from the bottom of the 2 by 4's on the form to the lower edge
of the inlet hole in the form will permit it to be set at the grade of
the house sewer. This frame is used to support the form for the tank.
To avoid caving the edges, drive the stakes supporting the frame before
beginning the excavation. The lumber in the frame can be used later to
make part of the tank baffles.
[Illustration: 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.
[Illustration: 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.