Disclosed is a method to mitigate deterioration of printing fluid in a tank of a printer. The method comprises: draining printing fluid from a tank of a printer, and stopping the draining before the tank is empty, wherein the printing fluid comprises solids suspended in imaging oil, filtering the printing fluid drained from the tank, to separate at least some of the solids from the imaging oil, passing the filtered imaging oil to a reservoir; and then passing imaging oil from the reservoir to the tank. Also disclosed is a printer and a system to perform the method.