I've read that a 1" bulkhead is good for 600gph.
The bit you need is a diamond hole saw or sometimes called a diamond core bit.
Yes, a 1" bulkhead USUALLY needs a 1 3/4" hole, but check the manufacturer to be sure. Glass shops in my area say "O yeah, no problem if it's not tempered" until I say "It's an aquarium and it's assembled" the they say "Oh, well maybe, I'm not sure, you'll need to bring it in for us to look at" and "instead of $10.00 per hole it will be $30.00 and not liable if it breaks during drilling or after refilling.
I'm just waiting on myself to buy the bit and try it. Other people do it, I think I can too. Still got more reading to do about it, and looking at portable drill stands to keep the bit square to the glass.
The bit you need is a diamond hole saw or sometimes called a diamond core bit.
Yes, a 1" bulkhead USUALLY needs a 1 3/4" hole, but check the manufacturer to be sure. Glass shops in my area say "O yeah, no problem if it's not tempered" until I say "It's an aquarium and it's assembled" the they say "Oh, well maybe, I'm not sure, you'll need to bring it in for us to look at" and "instead of $10.00 per hole it will be $30.00 and not liable if it breaks during drilling or after refilling.
I'm just waiting on myself to buy the bit and try it. Other people do it, I think I can too. Still got more reading to do about it, and looking at portable drill stands to keep the bit square to the glass.
I used Ornatapinnis's way, but I didn't buy a glass drill. I used an old 1 3/4 wood hole saw that I had. I first used the hole saw to drill a hole in a chunk of 3/8 inch thick acrylic i had laying around. I drilled the hole 3 inches over from the edge and 2 inches down from the top in the acrylic. I used this as my template to keep the drill from walking since I don't have a drill press. Then I ground the teeth off of the hole saw so I had a nice smooth edge. Most hole saw chucks have a removeable drill bit in the center. I took this out since you can't predrill glass. Put the clay down in a ring like Ornatapinnis said, set the template on top of the ring and press down to seal. I used duct tape to keep the tamplate from moving and used the rock tumbling slury to drill. I used a hand held drill and it only took me about 10 minutes per hole. Just make sure you keep the drill level and don't press too hard. I practiced on an old 55 that had a cracked bottom. I was nervous at first but it went pretty smooth. Nobody around here will touch tanks so you have to do it yourself. Hope this helps and saves someone some money.