sealant!

[kisstheground.livejournal.com]

Long story short, my friend and I nabbed a big KFC bucket to make a giant drinking glass for a friend for a holiday gift. We'd like to seal it so it will work as a cup with cold liquid in it (and a straw, naturally). What can we use to do this? Obviously, non-toxic, even with the jokes about killing him.
Anyone have any ideas?