Septic Tank Maintenance
Septic Tank
Cooperative Extension Service
College of Agriculture and
Home Economics
Maintenance
Guide M-113
R. Craig Runyan, Extension Water Quality Specialist
This publication is scheduled to be updated and reissued 11/07.
A septic tank is an underground sewage-collection
How Often Should You Pump?
system. The tank itself is a watertight container con-
structed of a sound, durable material resistant to cor-
This depends on the following:
rosion or decay.
•
Capacity of septic tank
When choosing a septic tank, your selection should
•
Flow of wastewater
be determined by the number of bedrooms or fixture
•
Volume of solids in wastewater
units to be served. New Mexico Plumbing Code re-
Volume of wastewater flow is determined by the
quires the following septic tank sizes:
type and frequency of common household activities.
Water conservation practices in the home will help to
Single family
Minimum septic tank size
limit the flow into the system. Use of an in-sink gar-
dwelling size
in gallons
bage disposal will increase the volume of solids. Care
0–2 bedrooms
750
should be given to the type and amount of solids dis-
posed of through a garbage disposal.
3 bedrooms
1000
Table 1 gives the pumping frequencies according
4 bedrooms
1200
to the size of the septic tank. Please note that biologi-
5–6 bedrooms
1500
cal and chemical septic tank additives are not neces-
sary and do not eliminate the need for pumping.
How Does a Septic Tank Work?
Table 1. Estimated septic tank pumping frequencies in
As the septic system is used, there is an accumula-
years (for year-round occupancy).
tion of solids in the tank, which is sometimes referred
Tank size
Household size (number of people)
to as sludge. The septic tank removes solids by hold-
(gal)
1
2
3
4
5
ing wastewater in the tank for at least 24 hours, allow-
750
9
4
3
2
1
ing the solids to settle and scum to rise to the top. This
1000
12
6
4
3
2
is accomplished by a series of baffles inside the tank.
1250
16
8
5
3
3
Up to 50 percent of the solids retained in the tank will
1500
19
9
6
4
3
decompose over time. Treated effluent water dis-
1750
22
11
7
5
4
charges from the tank to perforated drain pipes. From
Note: More frequent pumping needed if garbage disposal is used.
there, it drains to a constructed absorbtion or “leach”
field. The effluent eventually percolates through the
Safe Use of Septic Systems
subsoil to groundwater.
Do not put substances such as motor oil, gasoline,
Septic Tank Maintenance
paints, thinners, and pesticides in drains. These mate-
rials may pollute the groundwater and are toxic to the
As you use your septic system, sludge will accu-
microorganisms that maintain an active septic system.
mulate in the tank. Properly designed tanks have
enough space for up to three years of safe accumula-
Moderate use of household cleaners, disinfectants,
tion. Once the sludge has reached this level, the sepa-
detergents, or bleaches will do little harm to the sys-
ration of solids and scum no longer takes place, and
tem, but remember that where there is a high density of
sewage may overflow into the absorption area. This
septic systems there may be a cumulative impact on
can be prevented by periodically pumping the accu-
groundwater from household cleaners.
mulated sludge.
To find more resources for your business, home, or family, visit the College of Agriculture and Home Economics
on the World Wide Web at www.cahe.nmsu.edu
Fats, grease, coffee grounds, paper towels, sanitary
over your drain field may indicate trouble. Also, pay
napkins, disposable diapers, and other such items will
attention to slow-draining toilets or drains, sewage
clog your septic system.
odors, or sewage backing up into the house or over
the drain field.
Protect the Absorption Field
Checklist for Good Septic Tank Maintenance
Keep automobiles and heavy equipment off the ab-
sorption field.
• Check your system annually for leaks and
sludge.
Grass cover and shallow-rooted plants are beneficial
over the absorption field, but the deep roots of trees
• Have your septic tank pumped by a licensed pump-
and shrubs stress and may plug nearby drain tiles. Do
ing contractor.
not fertilize the soil above the drain field.
• Practice water conservation. Repair leaky
Grass on the surface of an absorption field should be
faucets and toilets. Spread clothes washing over the
mowed regularly to promote evaporation and removal
entire week, and operate only with a full load of
of water through the leaves. This helps prevent water
laundry.
from unnecessarily infiltrating the soil above the
absorbtion field.
• Learn the location of your septic systems. Make a
map and keep it handy.
Conserve Water
• Keep a maintenance record.
Remember to consider the capacity of your septic sys-
tem when installing new appliances or plumbing.
Limit the water entering the tank. Use water-saving
fixtures. Repair toilet float valves, leaks, and dripping
faucets.
Avoid Septic Tank Additives
Yeasts, bacteria, enzymes, and chemicals are sold
with the claim of helping septic systems work better;
however, there is no scientific evidence that additives
are effective. In fact, some cleaners allow the solids
in an overloaded tank to be re-suspended and clog the
drainage lines.
Additives are not an alternative to proper maintenance
and do not eliminate the need for routine pumping of
a septic tank.
Commercial biological additives are not necessary for
restarting decomposition after pumping because the
sludge residue contains active microorganisms.
How to Recognize Problems
Learn how to recognize problems with septic sys-
tems. For example, unusually lush and green grass
New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department
of Agriculture cooperating.
Reprinted November 2002
Las Cruces, NM
3C
Guide M-113 • Page 2
