Are you polluting your own backyard? You could be if you're not taking precautions with your septic tank. Here are guidelines and advice.

There's a certain out-of-sight, out-of-mind aspect to many household septic tank systems. "The main problems we see can be charged to neglect," said Steve Lindsey, owner of German Septic Tank Service in Greene County, Mo. "Many people don't think about their septic tank until stuff starts backing up in the system. By then a lot of damage may be done."

Lindsey sees a lot of home sewage systems in all stages. His company cleans more than 1,300 septic tanks and restaurant grease traps in a year's time. Some of them have been in use for years--long enough that the homeowner may not remember where the septic tank is located.

"The two problems we see most often are lack of maintenance and the integrity of the tank itself," agreed Bob Shultheis, University of Missouri agricultural engineer at Marshfield, Mo. "Often, little or no maintenance is done until toilets no longer flush right or sinks won't drain."

Shultheis estimates as many as two-thirds of the on-site waste treatment systems in southern Missouri are not functioning properly. Problems are potentially worse in the Ozarks region where soils are often thin and rocky and may allow partially treated sewage to leak directly into the groundwater.

"These [waste treatment] systems use bacterial action to break down raw human waste into by-products that are free of disease-causing organisms and pollutants before the treated liquids are released back to groundwater or surface water," Shultheis said. "When a system is working right, it does this very well. When it isn't working right, it may be polluting your own water well and the wells of several neighbors."

It may not be an appetizing comparison, but a septic tank with its disposal field acts pretty much like the human digestive system. Sewage from the home goes first into a large, water-tight chamber (the stomach) made of concrete or fiberglass. (Note: Steel septic tanks have been used in the past, but Missouri has legislation to eliminate their use.) Inside the tank, anaerobic bacteria partially break down the sewage. From the tank, sewage enters a network of perforated underground pipes (lower intestines) laid in trenches dug into the soil and back-filled with gravel. Most of the actual sewage treatment happens in this disposal field.

However, even in a well-functioning septic tank, there's always a portion of the waste that bacteria cannot digest. These collect in the bottom of the tank as "sludge." Grease and bits of paper float to the top as "scum."

"A septic tank should be inspected once a year, and the levels of scum and sludge in the tank should be measured," said Shultheis. "When the combined depth of scum and sludge make up more than the liquid depth in the tank, it needs pumping."

How often a septic tank should be pumped depends on the size of the tank, the number of people in the household and what kind of material goes into the tank. For example, tanks serving households with garbage disposals may need to be pumped more frequently. The table at right is a general guide to pumping frequency (in years).

"Some chemical products can kill the biological activity in your septic tank," said Dennis McEwen, owner of Ozark Mountain Septic Tank Cleaning, Lebanon, Mo. "Kitchen cleaners, chlorine bleaches and chemical drain openers are hard on the bugs in a septic tank. One of the most deadly substances is latex paint, which usually contains anti-microbial agents to retard the growth of molds and mildew. Just washing a couple of paint brushes in the sink can do in the bacteria in a system."

How about patent nostrums sold to "seed" bacteria in a septic tank? Do they do any good?

"Not much," said Shultheis. "At best, yeasts only help digest starch. They do nothing for the grease and other materials in a system. In a functioning septic tank, you'll have billions of bacteria at work. Adding a few million more from an envelope doesn't do a lot of good."

Even in a brand-new tank, naturally occurring bacteria will colonize the water in a matter of days, he adds.

Generally, the cost to pump out a septic tank averages $100, depending on the amount of work required. Installing a riser to extend the tank opening to ground level cuts this cost because it eliminates digging to uncover the tank manhole. Some county ordinances now require a riser on all new septic tanks, and a riser can be installed on an existing tank for about $25.

"Don't drive or park vehicles or heavy equipment over either the septic tank or the disposal field," cautioned Steve Lindsey. "And don't plant anything over the lateral field except grass."

A family of four typically uses 250 to 300 gallons of water every day. One of the simpler ways to protect a septic system--and increase the pumping interval--is to reduce the amount of wastewater flowing into it. This is especially important if the soil around your disposal field does not absorb water very well.

"Properly installed and maintained, a septic tank system should work almost indefinitely," said Shultheis. "The cost of regular maintenance and cleaning is cheap insurance compared with the expense of redoing an entire system."