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]