I would agree with wSelwyn - if you cut the bottom of a three-piece airlock it gets very rugged on the bottom. Expect it to be expendable at that point. It's also really annoying to cut!
The best solution for bucket brewers IMHO is Fermcap-S, you just add a few drops and don't have to worry at all:
But not a lot of people happen to have that kicking around, so hopefully a tube in the lid hole will work for you until it dies down a bit.
Hope you enjoy the kit!
Also, we do sell an AG version of Caribou Slobber: