For anyone needing to drill a lot of tanks, I found this hole saw guide to work very well and much less of a hassle than the guides I made.
There are much cheaper ones but they have very small suction cups.
That guide was used in conjunction with a water swivel similar to the one linked below. However, mine has a drill chuck instead of a collet and it has a small valve instead of just the nipple.
https://www.amazon.com/Almencla-Straight-Ceramic-Drilling-Watering/dp/B07P2JQRTP
The hole saws I use are the bonded diamond style where the diamond is dispersed through out the bonding material and is good for a 100 tanks or more (I have drilled hundreds of holes with mine). I know Jehmco carries them among others.
Even thin glass 2 1/2 gallon tanks drilled successfully with the setup mentioned.
Ken
