Secrets of the Septic System

If your home has a septic system you should know how it works — and how it might fail. Our correspondent provides an explanation.

| March/April 1989

septic system - full system diagram

The tank is an essential part of the septic system. The two-chamber design shown here is popular because it’s uncomplicated and reasonably effective. However, flooding or overloading the tank can still send undigested material into the drain lines, clogging the absorption field. The latest tank designs have deep holding chambers and internal convolutions to encourage solids to settle out from the flow.


Almost 60 million people in America practice inexpensive and effective home-scale recycling every time they run water. Individual, on-site sewage disposal systems — "the septic" to some country folks — do a commendable job of treating domestic waste through a natural biological process that eventually returns most spent water safely to its source. However, no septic system is perfect. Because of them, we tend to use too much water — perhaps 40% too much. Moreover, as long as the liquid is flowing in the right direction — out — we assume the plan is working, when in fact it may be broadcasting bacteria and discarded household chemicals.

The Dirty Truth

The boast of a homeowner who claims 20 years of trouble-free septic service is, sad to say, a shallow one. A properly designed septic system is supposed to receive occasional maintenance — usually nothing more than a cleaning every few years to remove accumulated insolubles. An untended unit can easily be overtaxed without a sign, quietly suffocating itself until it reaches a point at which it becomes less expensive to replace the system than to try to save it.

Then again, some systems are improperly designed or installed and cause their owners to face upkeep and expense beyond the norm. Frequent pumping, costly chemical treatments and mechanical handling systems shouldn't be necessary with a good installation.

Abuse of a system, however, will quickly lead to problems. No matter how conveniently paint thinners, cigarettes, hair, and harsh household cleaners go down the drain, they have no place there. Foreign — and especially nonorganic — material may never break down and can contaminate both the system and the local water supply.

Think of the septic system as a continuation of your household drain plumbing. Every water-bearing fixture in your home is connected by drainpipe to one main line that carries the highly diluted waste material to an air-and watertight septic tank buried a foot or so beneath the soil and at least 10 feet from the house.

The tank can be constructed of precast concrete, fiberglass, steel, and even stone or sealed brick. Average capacity is 750 gallons, though smaller tanks do exist. For large homes or households with more than five people or two baths, 1,000- and 1,500-gallon tanks are available.

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