I remember as a teenager seeing a movie a song that had the words:

          Workin' on the railroad, twenty cents a day
          Johnnie pick a tune on your banjo      [ plunk , plunk ]
          Listen to the wheels go clackin' on their way
          Tapioca, tapioca, tapioca they seem to say.

          Tapioca, tapioca, all I ever eat is tapioca,
          Tapioca, tapioca, all I ever eat is tapioca.         

I can't remember the movie nor the singer, but the tune and song still pop into my head regularly. Can anyone help? Google doesn't seem to have anything.