That's my 10G. Cut two holes for the returns, and slots for the overflow. Broke my first tank. My advice:
1) Use a multi-speed dremel, and the diamond tipped bits. I can't recall the part number, but they come in a pair for about 5 bucks at Walmart, one etching bit and one grinding bit.
2) Go
slooooow. I cracked my first tank because I didn't go slow. It's really easy to crack a 10G.
3) Use the etching bit to "drill" a hole in the tank. This will take as long as it takes to grind out the rest of the hole. Take your time, and let the bit do the work. Apply lots of water to cool the bit and glass, and to wash away the dust. This is where you are most likely to break your tank.
4) Use the grinding bit to "saw" the rest of your hole. Keep applying water, but use small up and down movements to walk the bit thru the glass around your mark.
I used masking tape on both sides of the glass where I was cutting to hopefully reduce the chances of a chipout. Plus, it's easier to mark where you want to cut on tape. I put a towel down under the hole I was cutting just incase the glass dropped out - I didn't want to risk it breaking the other side of the tank, but in every case but one the tape held the glass up when it finally cut thru. A dust mask might not be a bad idea. I also wore latex gloves. You will get a lot of glass dust on you.
Good luck!
