G'Day yerself. Is drathers the preferred word in Australia? "Ruthers" also shows up in the South (USA).
I would guess the words were rather old when Mark Twain put them in writing, since a word has to be in common usage before a teller of tales or a novelist would use them.
Only in the latest edition has the Oxford Dictionary attempted to include the Australian language. It has also made a better effort towards including some of the more difficult parts of the American language.