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Water Quality: Correct Use of Your Septic Tank

The septic tank is a storage tank where sewage is digested by bacteria. A well-designed, installed, and maintained septic tank disposal system functions well for many years.

A septic tank, sewage-disposal system consists of an underground, watertight receptacle (septic tank) and a soil absorption drainage field. Waste water leaves the home through an underground pipe connected to the septic tank. Baffles in the septic tank slow incoming waste water and prevent sewage from flowing directly through the tank.

How It Works

There are three levels in the septic tank:

  • Sludge, consisting of undigestible matter and heavy solids that will not float;
  • Liquid, which contains dissolved materials, such as detergents and small amounts of suspended solids;
  • Scum, made up of solids that float (grease and other lightweight solids).

Solids and scum in the tanks are digested or decomposed by anaerobic bacteria (bacteria active in the absence of oxygen). This decomposition liquifies up to 50 percent of the solids and scum. The liquid is carried out into the absorption field, and undigestible solids remain in the tank as sludge.

Each time raw sewage enters the tank, an equal amount of fluid is forced out of the tank. The fluid leaving the tank is called effluent and can contain disease organisms. Small amounts of suspended and dissolved matter (in the effluent) not completely stabilized or digested move out of the tank to the absorption field. Further digestion is carried on by bacteria in the soil of the absorption field.

The effluent is allowed to trickle into the soil in the absorption field. Never dispose of effluent directly onto the ground surface or into a body of water.

Precautions

For your septic system to work effectively, take appropriate precautions in everyday use of the system.

Do not dispose of the following substances in the septic system:

  • Coffee grounds
  • Dental floss
  • Disposable diapers
  • Cat box litter
  • Cigarette butts
  • Sanitary napkins
  • Tampons
  • Plastics
  • Facial tissues
  • Paper towels
  • Bulky wastes

Disposal of these items adds to the solids load and fills the septic tank more rapidly. This decreases efficiency and increases maintenance costs.

Avoid pouring liquid fats, grease, or oils down the kitchen sink drain. Fats and greases solidify and can block parts of the system. Also, avoid use of a garbage disposal in the kitchen unless the septic system is specifically designed to handle the extra load a disposal unit imposes. A garbage disposal can increase the solids load to the septic tank by 50 percent, necessitating more frequent pumping.

Keep toxic and hazardous chemicals out of the septic system. These include:

  • Paints
  • Varnishes
  • Thinners
  • Waste oils
  • Photographic solutions
  • Poisons
  • Pesticides
  • Herbicides

Moderate use of household cleaners, disinfectants, and bleaches does little harm to a septic system.

Do not use additives since they are of no benefit and some can do harm. Additives that cause accumulated sludge in the tank bottom to increase in volume result in the sludge being flushed out into the absorption field, plugging soil pores.

Remove the sludge and scum by pumping it out of the tank every 1 to 3 years -- for a 1,000-gallon tank serving a 3-bedroom home with 4 occupants and with no garbage disposal. Failure to have the septic tank pumped out regularly by a reputable service is the most frequent cause of damage to the absorption field. When the tank is not emptied, solids build up until they are carried along with the waste water into the absorption field where they clog soil pores. When this happens, a new drain field must be built.

Conserve Water

Excessive amounts of water entering the septic system increase the waste-water load on the absorption field and reduce the soil's capacity to absorb. Water flow to the septic system can be substantially reduced through water conservation; low-flow faucets, water-saving showerheads, conservation equipment for toilets, and water-saving appliances can be installed with a minimum of expense. Other hints for conserving water include:

  • Repair leaky faucets and toilet tanks promptly. Water leaking from the tank into the toilet bowl can waste up to 200 gallons of water a day.
  • Use dishwashers and washing machines only when they are fully loaded. Distribute washing clothes throughout the week to avoid overloading the drain field.
  • Do not let water run as you shave, shampoo, wash hands, brush teeth, or wash dishes.
  • Keep showers short, and reduce the amount of water used for baths.
  • Reduce toilet waste. The flush toilet accounts for about 40 percent of sewage wastes from an average home. Many flush toilets use 5 to 6 gallons of water per flush. Flush toilets that use much less water are available.
  • Teach family members water-saving practices.

For more information on water conservation, request from your county Extension office the free publication Water Conservation in the Home.

References

A Homeowner's Guide to Septic Systems, Virginia Water Resources Research Center, Virginia Polytechnic Institute, 1985.

Shelton, T. B., Septic System Care, Rutgers Cooperative Extension Service, Rutgers University.

Machmeier, Roger E., Get to Know Your Septic Tank, University of Minnesota, 1985.

Thompson, Carol Jo, Septic Tank Use and Care, Montana Cooperative Extension Service, Montana State University, 1986.

This material is based upon work supported by the U.S. Department of Agriculture, Extension Service, under project number 89-EWQI-1-9168.

By Dr. Frances C. Graham, Extension Housing Specialist

Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.

Information Sheet 1419
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director

Copyright by Mississippi State University. All rights reserved.

This document may be copied and distributed for nonprofit educational purposes provided that credit is given to the Mississippi State University Extension Service.
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