What are Septic Tanks Constructed of?

Have you ever wondered where does the water go when emptying a sink or flushing a toilet? If you live in a city, it is likely that the wastewater goes into a public sanitary gutter system to a plant for sewage treatment. However, if you live countryside with an undersized community, then it is probable that a septic system treats the wastewater in your area.

If you are curious to know how your septic system works, then read on. A septic system that runs correctly collects all the wastewater generated by the households (including showers, toilets, dishwasher, washing machine, sinks and so on), treats the wastewater to a safe level and returns the treated effluent to the groundwater system.

A standard septic system is comprised of a septic tank and a soil filter called a drain field. The function of a septic tank is to separate liquids from solids and to provide some breakdown of organic matter in the wastewater. A septic tank is a watertight container made from concrete, polyethylene or fiberglass. In the past, the tank was sometimes made of steel or wood. The size of the septic tank depends on the size of the house and household’s water use. Modern tanks are comparatively bigger than the older ones. Tanks may have one or two compartments.

The partially treated wastewater from the septic tank flows into the drain field. The drain field or the absorption field is a network of punctured plastic pipes laid in gravel trenches over a layer of soil.

Access risers extend the tank lids to or near the surface. Risers can be made of plastic or concrete and must be secured against entry since toxic fumes reside in the tank which can be a serious health hazard if left to escape. Installing access risers helps perform routine maintenance tasks easily. A more recent addition is a simple filter called an effluent filter. One installs it at the outlet of the septic tank to prevent large solid particles from flowing out of the septic tank and into the leaching bed.

In areas where good quality native gravel is scarce or prohibitively expensive, designers and contractors might consider installing gravel less absorption field system. Gravel less systems can be designed for a variety of home sites and under various conditions. These systems require the same maintenance as conventional drain fields and should include ports for inspection and clean out.

As the name suggests, gravel less system is an onsite system that does not use gravel in its drain field trenches or beds. Instead, these systems use large diameter o fiber-wrapped pipe, expanded polystyrene foam or chamber technology. Chambers are plastic domes that come in interconnecting segments of 60 or fewer inches long, 18 to 30 inches wide, and approximately 10 inches high. Modern excavators use chamber septic system in septic system trenches instead of the conventional “pipe and stone” (gravel) trenches.


Many modern homes use some or the other onsite treatment system to treat wastewater. The most common system involves a watertight septic tank followed by a conventional subsurface soil absorption system. Soil has a considerable capacity to transform and recycle wastewater. Soil absorption systems are reliable and the least expensive disposal option. Nevertheless, options in the form of chamber technology and usage of polystyrene foam are other alternatives. Experienced excavators know the difference and can determine which one suits a site the most.

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