The Collaborative International Dictionary of English v.0.48:

Floss \Floss\, n. [Cf. G. floss a float.]
   1. A small stream of water. [Eng.]
      [1913 Webster]

   2. Fluid glass floating on iron in the puddling furnace,
      produced by the vitrification of oxides and earths which
      are present.
      [1913 Webster]

   Floss hole.
      (a) A hole at the back of a puddling furnace, at which the
          slags pass out.
      (b) The tap hole of a melting furnace. --Knight.
          [1913 Webster]