Galziers use a hole saw similar to the one that are use on wood except they have diamond heads. They are pretty expensive too about 60 dollars. When drilling glass it is never a garunteed. Your best bet is to use a dremel tool. There are many articles floating aroung on the internet about them. I have a guy in my reef club that does it with no problem. He is doing my 20 gal
prop tank right now.
For reference a 1" bulk(drain) will give you about 600 GPH
. I don't like insump sump because they throw off way too much heat. I would go external if you have the room.