The Septic Tank

The septic tank is the first step of the wastewater treatment process

The septic tank is the first stop for all wastewater coming from the drains and toilets in your home. Bacteria, which are naturally present in all septic systems, begin to digest the solids that settle to the bottom of the tank, transforming up to 50 percent of these solids into liquids and gases. When liquids within the tank rise to the level of the outflow pipe, they enter the drainage system. The effluent then travels through a series of pipes into the drainfield where it is further clarified.

The septic tank is generally a watertight structure constructed of concrete or fiberglass. Manholes in the top of the tank allow access for inspection and pumping. Tanks also must have an inlet where wastewater from household plumbing enters the tank, and an outlet where effluent is discharged to the drainfield. Most newer systems have a baffle over the outlet that prevents large amounts of undigested solids from entering the drainfield.

A single-family home will have a tank anywhere from 500 to 1500 gallons in size. Larger tanks hold more, the added capacity can increase the time between necessary pump outs. If you are designing a septic system you would do well to consider a larger size septic tank.

There is a high incidence of failure in concrete tanks that consist of two pieces. The parts are generally “glued” together with a compound that, over time, will cause concrete to fail due to the acidic nature of the glue. Fiberglass tanks are lighter, easier to install, last longer, and some are constructed of thicker materials that are traffic rated, meaning they can be installed in areas that are driven over by vehicles.
Septic systems cannot dispose of all the material that enters the system. Solids that are not broken down by bacteria accumulate in the septic tank and eventually need to be removed. When the septic tank is not pumped out frequently enough, the solids can enter the pipes leading to and from the tank. This can cause sewage to back up into the house or cause the drain field to fail as the pipes and soil become congested. These problems are often costly to fix, pose a danger to public health, and are a significant source of water pollution. Companies who claim their products can eliminate the necessity for septic tank pump outs should be questioned.