Hole location for Herbie for overflow's

[Delphinus]

Are they schedule 40 bulkheads (black) or the schedule 80 (grey I would think)?

Can you post a picture of how far in they go into the hole?

I think you can drill over the holes if need be. You'll need a plant sprayer to spray water as you go instead of the usual trapping-water thing you usually have to do. I've used the spray bottle when drilling holes on glass I couldn't get horizontal like on a tank too big to turn sideways.

No idea how risky it is.

If it's just 1mm short maybe a dremel with diamond bit to grind out the holes to make them large enough?

Or, just use the 3/4" bulkheads but step it up to 1" on either side. Would make for a small restriction but maybe not much worse than a typical 90-degree thing.