I have a Skyy Vodka bottle that I made into a Waterfall. They have the same little notches on them as the sobe bottles.

And I never pull that thing out except as a party favor. It hits waaaayyy too hard to be used in normal smoking. The smoke is so thick and dense that even a baby hit hurts the lungs and starts you coughing.

I had a friend who didnt listen when I explained about the bong and playing nice with it, and took a huge rip out of it when it was passed over to him, and he sat outside for 30 minutes coughing and vomitting... and he wasnt trying to clear it either, it was just a decent sized normal hit, but huge for that bong.

I love me my gravity bong though. I dont smoke out of anything else if its just me. Made it from a Faygo bottle, and a tall plastic beer cup from a baseball game. Works like a champ.