a method for processing a flush - back fluid containing impurities after its use in a flush - back filter for cleaning fluid used in a cleaning process is accomplished in accordance with the invention in that flush - back fluid drawn from the flush - back filter is subjected to a sedimentation process and hereby acted upon at least from time to time by pressure and that after completion of the sedimentation process the flush - back fluid is separated in a pressure - tight manner from a least at least a portion of a sediment recovered thereby and the latter is subsequently removed and a part of the flush - back fluid cleansed at least to a large extent of impurities is returned to the cleaning process .