Here’s a recent thread on the process I helped out with!
I am drilling my 60g 24" rimless cube today! I have drilled only one hole, in a 20g aqueon, so I am nervous. I heard thicker glass should make it easier but I have some large holes to drill. With only 24" my space is really tight. My overflow has two - 2 3/8" - holes and I would like a dual...
www.reef2reef.com
Diamond coated glass hole saws do have a short lifespan… in my experience, you can get around 1-2” of cutting depth through glass before they really start getting dull, and really should be replaced for anything important you want to drill!
I recommend getting your diamond hole saw(s) diameter(s) based of the bulkhead fitting size(es), and style(s) you plan to use! — (For example, Hayward PVC plastic bulkhead fittings are fantastic, but typically do require a larger diameter glass hole than a generic bulkhead fitting made from ABS plastic!)
Good luck! Feel free to start a new thread on the process if you need any further advice!