I always wanted to try a Spiral Vase type print but hadn't found anything that I really liked. This form was posted on the Prusa forums by someone having trouble getting Slic3r to slice it in "spiral vase" properly. I tried it in Simplify3D and it came out well so I tried printing it.
It's nearly watertight except for a couple of spots on the bottom and one spot in the wall that got some grunge caught. I think a little wax coating inside would seal it up nicely.