Abstract: A solvent parts washer of the closed cycle type has an additional, independently controlled continuously cycled pump which recycles the solvent through a bypass filter. The pump has a suction inlet at the bottom of the parts washer bin and continuously passes a flow of solvent through the pass filter. This is one of a number of filters, commonly known as paper towel or paper roll filters, in which a liquid to be filtered is forced at a high pressure and low flow rate along the interstices between adjacent compacted sheets of a filtering medium. Such filter media and filters have relatively low flow rates because of their cleaning (filtering) capability is by absorption rather than screening, but have an exceptionally high ability to remove particles down to the sub-micron level from a filtered liquid. An agitator pipe in the solvent return flow serves to flush particulate contamination into the filter pump inlet. The invention maintains the solvent substantially free of contamination above the 0.