Here is what you need, these 2 bits, a dremmel, a nice jar or vase, downstem and slide. I can usually make a glass bong for 20 bucks or less, just depends on how nice you want to make it. I'm not sure how much the bits cost, as these were given to me, but I'm sure they wont be more than 20 bucks for both. First thing you do is figure out where to put the hole, using the diamond ball, drill all the way through the glass, the slower the better. Some people say fill the vase or jar with sand, and keep water on the hole while you are drilling, you can if you want, but i never do. After you have a hole through the glass, use the diamond cylinder bit and do circles with the dremmel to make the hole big enough for the downstem and grommet to fit snug and air tight. When it is the right size, wash off the glass dust, put the grommet in, and then the downstem and slide, fill with water, ice, or whatever you want, and have fun smoking out of a sweet glass bong you made in less than 30 minutes!
