Abstract: This disclosure is directed to apparatus for periodically purging contaminants from a coating liquid during a coating operation and, more particularly, for cleaning a doctor blade of an adhesive coater, the apparatus including a container having an open bottom defining with a surface of a rotatable transfer roll and a doctor blade a gap of a predetermined size which doctors the coating liquid or adhesive to a desired thickness prior to the application thereof to an article which is to be coated, and means for periodically increasing the predetermined size of the gap and returning the increased gap size to the predetermined size whereby particles otherwise incapable of passing through the gap when of the predetermined size will pass through the gap when of the increased size to thus maintain a relatively clean bath of liquid throughout a coating operation.