Abstract: A method and apparatus for backwashing filter elements in a filter vessel. At least one collapsible bladder in the form of a tube is suspended together with a plurality of filter elements in a mixture compartment of a vessel for filtering solids from a liquid-solids mixture, the tube having a volumetric displacement at least as great as the volume of filtrate required to flow from a filtrate compartment into the filter elements to slightly expand filter fabric enveloping the filter elements to disengage filtercake deposited thereon. Means are provided to fill the tube with fluid for expansion thereof and to rapidly empty fluid from the tube for sudden collapse of the tube and attendant rapid reverse flow of filtrate from the filtrate compartment.