| CAPACITIES, DIMENSIONS, AND CONCRETE MATERIALS FOR SEPTIC TANKS SERVING INDIVIDUAL DWELLINGS | ||||||||
| Maximum number of persons served | Liquid capacity of tank in gallons | Recommended inside dimensions | Materials for concrete 1:21/2:4 mix | |||||
| Width | Length | Liquid depth | Total depth | Cement sacks | Sand cubic yards | Gravel cubic yards | ||
| 4 or less | 500 | 3'-0" | 6'-0" | 4'-0" | 5'-0" | 16 | 11/2 | 21/2 |
| 6 | 600 | 3'-0" | 7'-0" | 4'-0" | 5'-0" | 17 | 13/4 | 23/4 |
| 8 | 750 | 3'-6" | 7'-6" | 4'-0" | 5'-0" | 19 | 2 | 3 |
| 10 | 900 | 3'-6" | 8'-6" | 4'-0" | 5'-0" | 21 | 21/4 | 31/4 |
| 12 | 1100 | 4'-0" | 5'-6" | 4'-6" | 5'-6" | 24 | 21/4 | 31/2 |
| 14 | 1200 | 4'-0" | 5'-0" | 4'-6" | 5'-6" | 25 | 21/2 | 33/4 |
| 16 | 1500 | 4'-6" | 10'-0" | 4'-6" | 5'-6" | 28 | 23/4 | 41/4 |
Figure 4.—Single-chamber septic tank. Note alternate use of baffle boards where sanitary tees are omitted at inlet and outlet.
The siphon provides intermittent discharge of effluent, which allows time for the disposal area to rest and aerate between discharges. This is more important where the discharge is nearly continuous than in small installations.
The frequency and volume of the discharge into the tile field are controlled by the sizes of the siphon and the dosage chamber. The dealer should be informed of the size of the tank and the number of persons in the household, in order that he may furnish the proper unit. A 3- or 4-inch siphon will be adequate for almost any farmhouse installation.
Construction
Most septic tanks are built of concrete cast in place, since in this way there is a minimum possibility of cracks developing. Concrete blocks, however (not cinder blocks), stone, brick, or structural tile are sometimes used. Prefabricated commercial tanks of concrete and various other materials also are available.
| SIPHON | |||
| Diameter of siphon | A - 3" or 4" | Clearance under bell | E - 2" |
| Diameter of bell | B - 10"or 12" | Distance across U-trap | F - 10" or 12" |
| Bottom of outlet to discharge line | C - 201/2" to 253/4" | Bottom of outlet to bottom of U-trap> | G - 12" or 13" |
| Drawing depth | D - 13" to 17" | Height above floor | H - 71/4"to 113/4" |
| DIMENSIONS OF DOSING CHAMBER | |||
| Number of persons served | Depth below discharge line[3] | Width[4] | Length |
| 4 or less | 161/4" to 201/4" | 3'-0" | 6'-0" |
| 6 | " | 3'-0" | 7'-0" |
| 8 | " | 3'-6" | 7'-6" |
| 10 | " | 3'-6" | 8'-6" |
| 12 | " | 4'-0" | 8'-6" |
| 14 | " | 4'-0" | 9'-0" |
| 16 | " | 4'-6" | 10'-0" |