Alot of people and even swip at one point have been frustrated with what to use for a bowl when making the famous "Gravity Bong' Well assuming you don't understand how to construct a gravity bong we will start from ground up but this thread is mostly focusing on the bowl. Constructing GB:----- Anyway take a 2 liter bottle or a bottle of sufficient size and cut the base off "or close to were the logo plastic ends" i will have a illustration image with this post aswell cut were the black line is on the bottom of the image. Basically you're 50% done, now just to make a bowl. Ahhhh finally the bowl:--------The bowl basic's are usually ok but somewhat frustrating and swim find's it hard to use a aluminum foil bowl as they tend to stick or melt or crumble when lifted, and alot of people just prefer to not smoke out of aluminum foil because of the health risk. Swim's idea for the Gravity Bong Bowl, it's simple and easy to use, only thing is you must already own a glass bowl for another piece such as a water pipe that is removable(,if not revert to https://drugs-forum.com/forum/showthread.php?p=101349#post101349 ) heat the plastic cap with a lighter and hold it with something maybe wire plier's so it doesnt burn you, slowly force your glass bowl through the top of the cap of you choice, the end result will leave a mold of your favourite bong bowl in the plastic cap and will be easy to lift up and get a hit without having to unscrew bottle caps or smoke from aluminum foil and pretty much last forever, or ofcourse as long as the glass. Well that's it folk's now ready to use, just fill a sink or bathtub , i prefer using a tea pitcher, with water, sink your 2 liter bottle in the liquid pack a bowl stick in the cap light it and pull it up the rest is self explanatory. Basic physic's of the project work as this, when the bottle is submerged in water the air has no place to go and the empty space that is not filled with water move's with the water, IE push the bottle down water goes up filling room were air was hence pushing air upward out of the cap of the bottle. When the bottle is fully submerged in water and then lifted up the water sinks slowly and the cylinder fill's with air molecules instead of water hence when u pull the bottle up the bottle sucks in air. I think that should be self explanatory. Do's:Remove bowl before placing bottle in water or substance in bowl will be thrown in the water by air pressure. Use common since, physics such as this is not rocket science. Dont's: slam the bottle in the water with a packed bowl already in it. K I warned you twice.