ever try a parachute? (i cant spell it) it basically the same thing as a gravity bong...but instead of water pulling the smoke put of the weed....u attach a plastic bag to the bottom of the 2L bottle (or w/e bottle u use) and pull the bag down....much bigger hits than a gravity bong. (use those bags that sliced bread comes in, and a 2L pop bottle...they work the best i find)