tanks are usually designed to hold enough sludge for up to three
years of normal operation. When the sludge level increases
beyond its designed capacity, sewage has less time to settle
before leaving the tank allowing more solids to escape into the
absorption field. Sludge infiltration into the soil
absorption field can result in system system failure. If
sufficient ground area is not available for repair/replacement of
the drain field, the home could be rendered inhabitable. To
prevent this, the tank must be periodically pumped (the material
pumped is known as septage) to remove the sludge buildup.
maintenance by homeowners is the most common reason for system
To work properly, the system should be properly installed by a
licensed contractor following local health department
The system should be regularly inspected and pumped** about
every three years or more depending on soil conditions.
Water conservation practices tends to prolong the life of the
system. For example, repair leaky faucets, fill the sink
to do dishes instead of running water continuously and do not
leave the water running while brushing your teeth. Excessive
water in the drain field prevents the soil from naturally
Do not divert roof drains, sump pumps, footing drains, etc.
into the system.
Never pour products such as gasoline, motor oil, or other
products not normally used with water down the drain.
It is a good idea to "space out" wash-loads to increase
the time over which harmful soaps and detergents are
introduced to the system. Your system will have a much
easier time treating 100 gallons of wastewater over 6 hours
than it would if all 100 gallons were dumped all at once.
The frequency of pumping will depend on:
the capacity of the septic tank
the volume of wastewater (also related to the size of the
the amount of solid material (such as produced by a garbage
disposal) in the wastewater
Estimated Pumping Frequencies (in years) For Year-round Residences (Calculated to provide a minimum of 24 hours of wastewater
retention assuming 50 percent digestion of the retained solids).
Tank Household size (number of people)
size 1 2 3 4 5 6 7 8 9 10
---------------Years between pumping--------------
500* 5.8 2.6 1.5 1.0 0.7 0.4 0.3 0.2 0.1 -
750* 9.1 4.2 2.6 1.8 1.3 1.0 0.7 0.6 0.4 0.3
900 11.0 5.2 3.3 2.3 1.7 1.3 1.0 0.8 0.7 0.5
1000 12.4 5.9 3.7 2.6 2.0 1.5 1.2 1.0 0.8 0.7
1250 15.6 7.5 4.8 3.4 2.6 2.0 1.7 1.4 1.2 1.0
1500 18.9 9.1 5.9 4.2 3.3 2.6 2.1 1.8 1.5 1.3
1750 22.1 10.7 6.9 5.0 3.9 3.1 2.6 2.2 1.9 1.6
2000 25.4 12.4 8.0 5.9 4.5 3.7 3.1 2.6 2.2 2.0
2250 28.6 14.0 9.1 6.7 5.2 4.2 3.5 3.0 2.6 2.3
2500 34.9 15.6 10.2 7.5 5.9 4.8 4.0 3.5 3.0 2.6
If you have just moved into a home
and do not know the tank capacity, it is wise to have the tank
pumped and inspected. In order to extract all the material from
the tank, the top scum layer must be first broken up. The
sludge layer is then mixed with the liquid portion of the tank by
alternately pumping liquid from the tank and re-injecting it
into the bottom of the septic tank. The tank should be pumped
through the central manhole and not through the baffle ports.
If the baffle ports are damaged, this could eventually lead to the
destruction of the leach field. The baffles prevent the
floating scum from exiting the tank. If pumping is too infrequent,
(even if the tank is not completely clogged with solids) the
reduced liquid volume in the septic tank cuts settlement time
forcing small floating solids prematurely into the drain field.
Decomposing septic tank waste produces toxic gases which can kill
a human in minutes.
When servicing a tank, be sure
the area is well ventilated and never go into a septic tank to
retrieve someone who has fallen in without a self-contained
breathing apparatus (SCBA). If this occurs and a SCBA is
unavailable, call emergency services and place a fan at the top of
the tank to supply fresh air.