the diamond core bit is $12.00 on ebay and drilling is much easier than you'd think. the thicker the glass, the easier. I was always afraid and built all kinds of crazy PVC self draining syphons.....in the end, a hole in the bottom of the tank is the easiest way to go. Start the drill pretty slow rpm, approach the glass at a 45degree angle, the bit will start to bit and you can level out the bit. dont push, let the diamonds and the weight of the drill do the work. Maybe slight pulsing motions if its taking a long time. Keep the hole hydrated either with a damn made of putty or just have some water in the bottom of the tank (1/4" or so) it will sink through effortlessly, like a spade bit through plywood. For 20 buck worth of pvc through-hull fittings and a bit, you can turn your tank into a drilled tank with a sump. Sumps are great places to grow plants, or treat the water. the water enters the main tank from the pump in the tank below, and the hole in the bottom has a 1" slip fitting with a length of PVC long enough to always keep the display tank filled. No 2" scumlines near the top like in fresh water tanks. The only tank that needs to be monitored is the sump.