The Septic Tank

The tank itself ranges in size, with 1,000 gallons being a standard. The overseeing regulatory agent, like the health department, usually determines how big a tank must be.

One person can use 50 to 350 gallons of water per day for drinking, washing, flushing the toilet, and cooking. Since water is the biggest filler of a septic tank, the number of people living in a home usually determines tank size.

The tank itself is large, waterproof, and airtight. Tanks are made from precast concrete, plastic, steel, fiberglass, or other material.

The configuration of the site sometimes dictates what kind of tank to use. Again,the regulatory agent can help make this determination.

The tank is buried underground some distance from house. It should not be run over by vehicles.

Lines run from the house to the septic tank. The tanks are located so that gravity sends the water into the tank. Another line from the tank goes away from the house to the drain field.

Tanks generally have two compartments, though some engineers are now leaning toward a single compartment.

The septic tank design is such that a still pond is created as wastewater enters the tank chamber. This becomes a breeding ground for bacteria, yeasts, and fungi.

As organic solids sink to the bottom of the tank, the microbes attack the solid waste. This produces methane and other gases as a by-product.

If a tank is working properly, the bacteria are busy all the time, though they might slow down in freezing weather. A well-designed tank can remove more than 50 percent and possibly as much as 90 percent of the solids.

The septic tank has five functions. It:

- receives the wastewater from the house

- separates the solids from the liquids

- stores the solids

- decomposes the solids

- sends the effluent wastewater out to the drain field.

If a tank is not properly installed, the flow of the wastewater can be impeded. This can allow solids to flow into the drain field. This can be a sign of tank failure.

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