as those for plumbing plans. These symbols are
for a small septic tank are shown in figure 3-17. A
covered in the preceding section. Typical building
larger tank is shown in figure 3-18. An integral part
connections are shown in figure 3-13. If you study
of septic tanks is the dosing tank which is usually
figure 3-13, you will note the amount of information
constructed of wood or concrete. When wood walls
supplied to the plumber. Note also the specific
are used, a concrete slab floor is favored as giving the
information given on the caulking and sealing of
best foundation for installation of the intermittent
joints for each type of drain. These are standard
siphon. Plan and elevation views of a dosage tank
detail conventions and will be found on all properly
are shown as part of the septic tank details in view A-
prepared sewerage plans. Figure 3-14 illustrates the
A of figure 3-18.
conventions used in a typical sewerage system plan.
You can see that this is not a simple system;
Installations which are
c. Imhoff Tank.
however, it is typical of large-job sewerage systems.
sufficiently complex to require a treatment plant will
Note that reference is made to the actual building
normally have plans prepared for a specific site,
plans for the details of the house drain connections.
accounting for the topography and soil conditions.
Where a septic tank is not adequate to handle the
load, an Imhoff tank may be used.
Typical
3-11. MANHOLES
construction details for a concrete Imhoff tank are
Manholes are generally of circular cross section
shown in figure 3-19.
when made of cement-plastered brick-and-mortar
walls set on a concrete base slab. The top is closed
3-13. DISPOSAL FACILITIES
with a removable heavy lid that lays in a cast-iron top
ring. Where manholes are made of wood the cross
a. Leaching Tanks. The receivers of raw
section is square or rectangular and has a removable
sewage or septic-tank effluent are leaching tanks or
cover set in the roofing timbers. An example of
cesspools and can be made of 4-by 4-inch lumber or
manhole construction is shown in figure 3-15. Note
5-inch round timbers. Dry masonry may be used for
that the manhole depicted is made of brick or
wall construction where time and materials permit. A
concrete and is circular. From the dimensions given,
design for a small leaching tank is shown in figure 3-
you can see that the base slab slopes (10 inches to 9
20.
inches). The lid is 2 feet, 4 inches in diameter and
3/4 inch thick. There are three shelves around the
b. Sand-Filter Fields. Either vitrified clay or
pipes in an opening whose diameter is 3 feet, 6
concrete drain tile, without sealed joints, is used for
inches.
piping in both subsurface irrigation and subsurface
sand-filter disposal systems.
Approved design
methods, giving plans and profiles, for installation of
3.12. SEWAGE TREATMENT
drain tile in the two types of irrigation and sand-filter
a. Grease Traps. Wooden box type grease
fields are shown in figures 3-21 and 3-22.
traps are generally set in the flow line of the house or
building sewer to intercept greases and fats from
(1) Distribution boxes. To change the
kitchen sinks. Baffles are placed in the boxes to
flow of effluent to different sections of a filtration
collect floating grease particles but arranged so as not
field, a distribution box is used and can be made of
to restrict the flow of the effluent. Figure 3-16 shows
wood, concrete, or brick. The diversion gate is
the general design of a grease trap.
usually of wood, with a handle-slot, so that its
position in the distribution box can be moved to
These are usually
change the sewage flow direction. See view B-B on
b. Septic Tanks.
constructed in box-section form of lumber. Concrete,
figure 3-18 for the installation requirements of a
brick, or stone may be used for more permanent
distribution box.
installations where such materials are available.
Single building tanks of about 500-gallon capacity
(2) Size. Figures 3-18 and 3-23 illustrates a
are sometimes made of steel and supplied ready for
typical small sewerage system which
installation in the sewer system. Construction details
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