The septic tanks are prefabricated watertight and impermeable equipment that allows the sedimentation and elimination of suspended solids from toilets, washbasins, kitchens, etc., and their transformation into inoffensive and inoffensive mineral compounds, through decanting and solubilization by the action of anaerobic bacteria (digesters).

To limit the discharge of solids into the septic tank effluent, two-compartment tanks are used. Depending on the pollutant load, three compartments may be available using one as a sump and grease separator.