[3] Depending upon depth C of siphon.
[4] Same as single chamber tank [fig. 4].
Figure 5.—Typical design for a concrete septic tank with a dosing chamber and a siphon.
Masonry units should be laid in full beds of 1:3 cement mortar and the walls and floor plastered with at least a 1/2-inch coat of 1:2 mortar. Cells of concrete blocks and tile must be filled with concrete. Masonry walls are generally 8 inches thick, and care must be taken to follow inside dimensions given for concrete tanks. Directions for laying structural tile, brick, and concrete blocks can be obtained from dealers or trade associations.
Commercial tanks are suitable if they embody the essential features given in this bulletin. Capacities should be as recommended in [figure 4] for concrete tanks. Proper installation and periodic servicing also are essential. Tanks badly damaged in handling should not be used. Rapid corrosion of steel tanks will result if the asphalt coating is impaired. Minor defects in precast masonry tanks may often be overcome by plastering the interior with cement mortar.
BUILDING A CONCRETE TANK[5]
[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.
