The Collaborative International Dictionary of English v.0.48:

Sinking \Sink"ing\,
   a. & n. from Sink.
   [1913 Webster]

   Sinking fund. See under Fund.

   Sinking head (Founding), a riser from which the mold is fed
      as the casting shrinks. See Riser, n., 4.

   Sinking pump, a pump which can be lowered in a well or a
      mine shaft as the level of the water sinks.
      [1913 Webster]