Making a big hole in a perfectly good tank.
I'm stting this system up with a low profile drain offset to one side away from from the back. Since it won't have a side to attach it to to keep it in place and a lot of rock setting on top of it, I'm adding a second sheet of glass on the bottom to add additional strength to the bottom.
I prefer to start by making a wood template or jig. Jigs will keep the bit in place and stop it from "walking". If drilling multiple holes a jig helps keep all the holes aligned also. The diamond bit works just as well with wood as glass (no water is required to cool it
)
Sometimes I'll use clamps (use wood on both sides of glass to protect it) but most of the time I use weights like I did here to hold a jig (and hose) in place while drilling.
Reinforcing glass piece with hole.
Silicone and setting the reinforcing piece in place. After it set up a few days I went around the edge with more silicone.

Drilling out the bottom. To keep the bit cool I added about 1/2" of water. The tank is sitting on a hydralic cart, to help keep the bit from chipping when the bit broke through I placed several layers of cardboard compressed under the location of the hole. The cardboard also helped keep water draining out to a minimum after the hole was completed.
Checking to make sure I drilled the right size hole.
