The best way is forget the propane tank and use something else.  I've been told, by guys with enough experience I listen to them, that the tank itself will absorb the odorant used to give propane it's stink.  It may eventually go away, but it might hang around a long time.

If you take out the valves and roll it over and a yellow oily substance runs out ... don't get it on your boots or they will smell like ethyl marcaptan until the day you burn them.