The Collaborative International Dictionary of English v.0.48:

Gong \Gong\, n. [AS. gong, gang, a going, passage, drain. See
   Gang.]
   A privy or jakes. [Obs.] --Chaucer.
   [1913 Webster]

   Gong farmer, Gong man, a cleaner of privies. [Obs.]
      [1913 Webster]