You can sometimes also tell if glass is tempered if you have polarized sunglasses. It should have a wavey or swirl apperance to it. If you have ever driven in your car and looked at your side windows you'll know what I am talking about.
Drilling a tank isn't really all that hard. You need a diamond coated hole saw and a drill, some way to keep the glass cool (usually water) go slow, and let the drill do the work. I sure some member close to you has the proper tools and would let you borrow them.