Abstract: Sintered glass pellets which generally decrease in particle size as they increase in specific gravity provide a unique filter medium which varies from larger pellets at its inlet (upstream) upper portion to smaller pellets at its outlet (downstream) lower portion. In view of the variation in specific gravity, particles forming the filter medium generally resume substantially their initial respective positions after the medium is back-flushed for cleaning. Although pellets throughout the medium differ in specific gravity, they are made of the same ingredients. The individual pellets are formed by granulating finely-ground glass with a suitable binder and sintering the resulting granules.