Ahhh, forgot to add....wax the cork end. Sorry.
I didnt invent the trick, its an old one similar to what ive seen done for pocket flasks in the way back days when a cork could break in an actual pocket...an old one I examined actually used a long thin theaded eye bolt instead of a cotter key, and had a matching gromet that it threads into on the other end. You can then tighten up the cork (bulging it in the center) with the finger ring attached to the eye bolt so that it is actually more water tight than a loose dried out cork might otherwise be...again, its a trick used on old pocket flasks.
tc