The Collaborative International Dictionary of English v.0.48:

Soaker \Soak"er\, n.
   1. One who, or that which, soaks.
      [1913 Webster]

   2. A hard drinker. [Slang] --South.
      [1913 Webster]

WordNet (r) 3.0 (2006):

soaker
    n 1: a heavy rain [syn: downpour, cloudburst, deluge,
         waterspout, torrent, pelter, soaker]
    2: a person who drinks alcohol to excess habitually [syn:
       alcoholic, alky, dipsomaniac, boozer, lush,
       soaker, souse]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "soaker":
   alcoholic, alcoholic addict, bacchanal, bacchanalian, bibber,
   big drunk, boozehound, boozer, brash, burst of rain, carouser,
   chronic alcoholic, chronic drunk, cloudburst, deluge,
   devotee of Bacchus, dipsomaniac, downfall, downflow, downpour,
   drencher, drinker, drunk, drunkard, flood, gushing rain, guzzler,
   hard drinker, heavy drinker, heavy rain, imbiber, inebriate,
   lovepot, lush, oenophilist, pathological drinker, plash,
   pot companion, pour, problem drinker, rainburst, rainspout,
   rainstorm, reveler, scud, serious drinker, shikker, soak,
   soaking rain, social drinker, sot, spate, spout, swigger, swiller,
   thirsty soul, tippler, toper, torrent of rain, tosspot, wassailer,
   waterspout, winebibber