Making a drinking cup from bamboo?

I just cut some fresh, live bamboo and would like to make some drinking cups from the fatter poles. I say you just cut it, sand down the rim and drink from it using a straw. My friend says we need to "dry" it and then coat the inside with some kind of non-toxic sealer. I don't remember them using any sealers on Gilligan's Island when they made cups from coconut shells. Anyone ever do this and can you just drink straight from them without any "processing"? I've looked online but can't seem to find what I want.