Here’s a recent thread on the process I helped out with!
https://www.reef2reef.com/threads/drill-time.1117917/
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!