I just received some interesting information from Aqueon, the makers of "All Glass Aquariums" that will prove helpful to members who are planning to drill their tanks for external plumbing. We all should know that you will destroy your tank if you attempt to drill a hole in the glass when the glass is tempered. I purchased a brand new Aqueon tank from Craig's list. It has all the stickers on it and the upc label and has never had water in it. The people selling it decided they wanted something larger. I bought it to replace a Plexiglas tank that the center support across the top of the tank broke in the middle of the night and instantly turned it into a Bow front tank. Unknown manufacture, but thankfully no water escaped. I sent an Email to Aqueon to inquire as to the type of glass this tank is made from. What they told me was, "If the tank was manufactured within the last two years AND it was purchased as a stand alone tank as opposed to a tank kit that comes with lights, hood, heater, gravel, food, etc. It only has tempered glass in the bottom. If purchased as a complete kit, the entire tank is manufactured with tempered glass." No reason was given for the two different build types. They also said if the tank is older than two years they cannot tell you for sure what type of glass was used as employees "could" have used either during the production process.