A method for extracting a liquid additive from an interior space of a tank at an extraction point includes: filtering the liquid additive by at least one filter that covers the extraction point and that is configured to separate the extraction point from the interior space of the tank and through which the liquid additive flows, wherein contaminants of the liquid additive are deposited on a surface of the filter, and extracting the liquid additive from the tank at the extraction point; forming at least one porous filter cake from contaminants of the liquid additive on the surface of the filter; and filtering the liquid additive by the at least one porous filter cake, wherein contaminants of the liquid additive are deposited in the filter cake, and extracting the liquid additive from the tank at the extraction point.