all you need to know is:
-use a rasp-type bit
-Dremel tools are great. Corded is better than corded. Better speed.
-Fill the vase that you want to make a bong out of with water. And hold it so that where you are going to drill is also just barely under water. A big tupperware works great for this.
-heat or pressure causes glass to crack and the bit to get dull.
-work gently with the hole just at the surface of the water and always wear your safety glasses because little glass dust and shards go everywhere.