Untreated wastewater from a property flows into the septic tank, where the solids separate from the liquids. Some solids, such as soap scum or fat, will float to the top of the tank to form a scum layer. Heavier solids, such as human and kitchen wastes, settle to the bottom of the tank as sludge. Self forming bacteria in the tank help the system “digest” these solids or sludge. The remaining liquids flow out of the tank to a land drainage system or drain field. Baffles built into the tank hold back the floating scum from moving past the outlet of the tank. It is generally recommended that septic tanks be pumped out annually, or the sludge and scum layers be measured at least every year so that solids don’t wash out into the soil treatment system. Solids can clog the soil and limit its ability to properly treat the septic-tank effluent.

There should also be a vent pipe from the first stage chamber and preferably the second stage as well to vent any gasses, that rise from the sludge, to atmosphere. Suitable covers should always be placed completely over a septic tank capable of withstanding an adult’s weight, and to avoid children / animals falling into the tank. (Sometimes it pays to have light duty covers over the tank and to place a lockable strap over the covers.)

The effluent from a septic tank, still contains about 70% of the polluted matter in the sewage, and hence there is a need for further treatment of the liquid from the tank.