Biological pits for the region Emilia Romagna in polyethylene for wastewater from domestic toilets. Imhoff tanks in Emilia Romagna are designed to retain solids and are used to carry out an initial treatment defined as primary treatment. These imhoff tanks are made entirely of polyethylene and are of the vertical type and are sized for 3 to 48 equivalent inhabitants. Imhoff pits have a smooth, thick or corrugated surface, designed to suitably resist backfilling operations. Imhoff pits have provisions for wastewater inlet and overflow. In the upper part there