Abstract: A partition includes a float on its upper edge and a partition which divides the inside of a container into two compartments. The perimeter of the partition contacts the walls and bottom of the container using a U-frame that is provided with three flexible bands. In one of the compartments, anchored on a support, are filters arranged together with the supports. An external pump transfers liquid from the bottom of one compartment to the bottom of the other compartment and channels the liquid between the flexible bands and below the partition in a uniform and calibrated manner over its entire length. At the same time, liquid passes from this second compartment to the first one above the float. The float meters and calibrates the liquid flow over its entire length, thereby generating a surface stream which discharges into the filters.