The Collaborative International Dictionary of English v.0.48:

Drain \Drain\ (dr[=a]n), v. t. [imp. & p. p. Drained
   (dr[=a]nd); p. pr. & vb. n. Draining.] [AS. drehnigean to
   drain, strain; perh. akin to E. draw.]
   1. To draw off by degrees; to cause to flow gradually out or
      off; hence, to cause the exhaustion of.
      [1913 Webster]

            Fountains drain the water from the ground adjacent.
                                                  --Bacon.
      [1913 Webster]

            But it was not alone that the he drained their
            treasure and hampered their industry. --Motley.
      [1913 Webster]

   2. To exhaust of liquid contents by drawing them off; to make
      gradually dry or empty; to remove surface water, as from
      streets, by gutters, etc.; to deprive of moisture; hence,
      to exhaust; to empty of wealth, resources, or the like;
      as, to drain a country of its specie.
      [1913 Webster]

            Sinking waters, the firm land to drain,
            Filled the capacious deep and formed the main.
                                                  --Roscommon.
      [1913 Webster]

   3. To filter.
      [1913 Webster]

            Salt water, drained through twenty vessels of earth,
            hath become fresh.                    --Bacon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

drained \drained\ adj.
   having lost much energy or emotion from vigorous activity; --
   of people; as, the day's events left her completely drained
   of strength.
   [WordNet 1.5]

   2. having resources completely depleted.

   Syn: depleted.
        [WordNet 1.5]

   3. having no power remaining; -- of a battery.

   Syn: run-down.
        [WordNet 1.5]

   to go down the drain

   1. to be consumed in profitless activity; to be wasted; to
      become worthless.

   2. to vanish or cease existing.
      [PJC]

WordNet (r) 3.0 (2006):

drained
    adj 1: emptied or exhausted of (as by drawing off e.g. water or
           other liquid); "a drained marsh"; "a drained tank"; "a
           drained and apathetic old man...not caring any longer
           about anything" [ant: undrained]
    2: very tired [syn: knackered, drained]
    3: drained of electric charge; discharged; "a dead battery";
       "left the lights on and came back to find the battery
       drained" [syn: dead, drained]

Moby Thesaurus II by Grady Ward, 1.0:

130 Moby Thesaurus words for "drained":
   ablated, acarpous, all in, arid, ausgespielt, barren, beat,
   beat up, beaten, blanched, bleached, bleached white, bone-weary,
   burned-out, burnt up, bushed, cachectic, celibate, childless,
   consumed, dead, dead-and-alive, dead-tired, deadbeat, debilitated,
   decolored, decolorized, depleted, desert, desolate, devitalized,
   disabled, dissipated, dog-tired, dog-weary, done, done in, done up,
   drained of color, dried-up, dry, eaten up, effete, enervated,
   enfeebled, eroded, eviscerated, exhausted, fagged out, failing,
   fallow, fatigued, feeble, finished, frail, fruitless, gaunt,
   gelded, gone, healthless, impotent, impoverished, in poor health,
   incapacitated, ineffectual, infecund, infertile, infirm, invalid,
   issueless, jejune, knocked out, languishing, leached, lightened,
   menopausal, moribund, nonfertile, nonproducing, nonproductive,
   nonprolific, pale, peaked, peaky, played out, pooped, pooped out,
   prostrate, ready to drop, reduced, reduced in health, run-down,
   sapped, sickly, sine prole, spent, sterile, sucked dry, teemless,
   tired out, tired to death, tuckered out, uncultivated, unfertile,
   unfruitful, unhealthy, unplowed, unproductive, unprolific, unsound,
   unsown, untilled, used up, valetudinarian, valetudinary, virgin,
   washed-up, waste, wasted, weakened, weakly, weary unto death,
   whacked, whitened, wiped out, with low resistance, without issue,
   worn, worn away, worn-out