Source : Webster's Revised Unabridged Dictionary (1913)

Unclog \Un*clog"\, v. t. [1st pref. un- + clog.]
   To disencumber of a clog, or of difficulties and
   obstructions; to free from encumbrances; to set at liberty.
   --Shak.

Source : WordNet®

unclog
     v : become or cause to become unobstructed; "The chemical that
         we poured down the drain unclogged it" [ant: {clog}]
     [also: {unclogging}, {unclogged}]