The modern septic tank is a watertight box divided into two compartments and usually made of precast concrete, concrete blocks or plastic. When household waste drains into the box, several things take place. Organic solid material floats to the surface and forms a layer called the "crust". Bacteria in the septic tank biologically convert this material to liquid. Inorganic or inert solid materials and the by-products of the bacterial digestion sink to the bottom of the tank and form a layer called "sludge". Only fairly clear water should exist between the crust and sludge layers. This clear water - and only this clear water - should overflow into the second compartment and then out to the soil absorption area.

If the sludge in your system is not removed, it will eventually overflow into the second compartment. This will clog the system and it will need to be replaced, at enormous expense and inconvenience. The second part of septic system maintenance involves the bacteria necessary for solids digestion. If bacteria-killing products - such as bleach, disinfectants, drain openers, detergents, etc. - are used in the home, the bacteria must be replenished, in order to avoid the disastrous build-up and overflow of solids. Your septic tank could be overflowing solid material into the soil right now, and you won't know until it blocks the soil so badly that no more drainage is possible. This blockage takes varying periods of time depending on soil structure. But these are the facts: a neglected system will get blocked; it will overflow; it will have an obnoxious odour; it will contaminate and pollute the surrounding area. It will probably have to be replaced. The first septic system emergency usually marks the beginning of the end.