filtration

filtration
    n 1: the process whereby fluids pass through a filter or a
         filtering medium
    2: the act of changing a fluid by passing it through a filter
    

Filtration \Fil*tra"tion\, n. [Cf. F. filtration.]
   The act or process of filtering; the mechanical separation of
   a liquid from the undissolved particles floating in it.
   Fimble
    

38 Moby Thesaurus words for "filtration":
      bolting, clarification, colature, destructive distillation,
      distillation, edulcoration, effusion, elution, elutriation,
      essentialization, excretion, exfiltration, extraction,
      extravasation, exudation, filtering, leaching, lixiviation, ooze,
      oozing, percolating, percolation, purification, refinement,
      riddling, screening, seep, seepage, separation, sieving, sifting,
      spiritualization, straining, sublimation, transudation, weep,
      weeping, winnowing