Conventional Septic System
A conventional septic system consists of a septic tank and three-inch or four-inch perforated drainfield pipe. The sewage enters the septic tank where the solids settle on the bottom of the tank, the grease floats to the top of the tank and the sewage is partially treated by anaerobic bacteria. In a properly designed, dual-compartment septic tank, the partially-treated sewage gravity flows from the primary compartment, where most of the solids are removed, through a baffle into the clarifier compartment and out of the tank from the clear zone (the level at which the fewest solids are present) to the drainfield.
Conventional drainfields commonly are constructed using four-inch sewer and drain pipe installed in gravel-lined trenches or using eight-inch graveless drainfield pipe that is surrounded with a geotextile fabric “sock”. While the cost of using either is comparable, the ease of handling renders the use of graveless pipe a less labor intensive one for the installer. Four-inch pipe and gravelless pipe perform equally well in Class 1b, Class II or Class III soils assuming the absence of soil or site constraints prohibiting the use of either.