SEWERAGE
From page 38
apportioned two-thirds to
one-third, should have a
volume of 2 520 litres and
should be adequate for the
daily needs of up to six
people.
Such a tank would have
internal dimensions of 1,0m x
2,1 m x 1,2m deep.
For eight people the size
should be 1,1 m x 2,2m x
1,3m deep (volume 3 146
litres).
For ten people the size should
be 1,1 m x 2,5m x 1,3m
deep (3 575 litres).
For 12 people the size should
be 1,2m x 2,4m x 1,4m deep
(4 032 litres).
For 16 to 20 people the size
should be 1,2m x 2,6m x
1,4m deep (4 368 litres).
If your kitchen sink is fitted
with an automatic waste
grinder these volumes should
be increased by 30%.
If building one's own tank
from brick the walls should be
at least 230mm thick, and
Here are the correct sizes for a standard
two-chamber septic tank system
plastered on the inside.
The floor, which should be a
single-cast concrete slab,
should also be plastered.
The dividing wall (between
the two tanks) can be a single
brick thick, with two holes
measuring 230mm x 80mm
(equivalent to one brick) sited
halfway between the top and
the bottom of the tank. There
should be a small space
between the top of this wall
and the roof of the tank to
allow gas to flow back and
forth between the two tanks.
The primary and secondary
tanks need not be adjoining
but can be some distance
apart and joined by pipe,
depending on the topography
and soil conditions, as long as
the above criteria are fulfilled.
The end of the inflow pipe
from the house should be
50mm higher than the
outflow pipe to the soakaway
correctly apportioned tanks
fitted with suitable piping.
More sophisticated dig-andor drain field.
drops exist, however, which
Both the inflow and outflow
function as mini-sewage
pipes should be fitted with a
works, cleaning the effluent to
T-piece. One end of the T
a far greater degree than a
should extend into the fluid
conventional septic tank and
and the other should stick up rendering the final fluid
in the air as a gas escape.
suitable for use as irrigation
Another common fault is to fit water or for discharge into
the roof of the tank with only rivers and streams.
one manhole over the
These systems are more
primary tank. Two manholes
complex. They are divided
should be fitted, one over
into five or more chambers,
each tank, to enable them
including two which function
both to be emptied comas primary and secondary
pletely by pumping.
septic tanks, another which is
The roof of the tank should
filled with plastic media and
be of reinforced concrete, not an air pump and functions in
corrugated iron etc, which
much the same way as a
will rust and become
municipal sewage aeration
dangerous.
system, and yet another tank
The alternative to building
from which reactivated
one's own tank is, of course,
sewage sludge, containing a
to buy a ready-made plastic
concentration of beneficial
digester system.
microbes, is pumped back
In their most basic for these
hydraulically into the septic
are merely “dig and drop”
chamber as a “booster”.
containers divided into
40
www.sasmallholder.co.za