Coconut bongs are hype, so far I have constructed two of them. Here are some pics of my first coconut bong, it's not nearly as professional as my most recent one (I gave the new one to my brother for christmas).

This one I sadly cut in half to get the meat out of it, putting it back together was a pain and a half. I used a metal pen tube as the stem, it's the perfect diameter though, bowls just slide into the stem without screwing and they actually stay there. I used bathroom clear caulking to hold the stem to the coconut, so far so good, it hasn't melted, burned or given off noxious fumes. I meant for this to be a water bong, but you get a lot of splash back so it's just a regular bong. The inside and outside have been coated in urethane, which once dried doesn't give off fumes and is water proof.

I'll check if I have some pictures of the other coconut bong... it's so much better... proper gromets holding a proper stem in place, it has a choke hole, and it wasn't cut in half!