Felix,
I can't say with any degree of certainty but it *appears* kinda iffy IMO
That said, I've seen far worse hold for a long time so... hard to say with certainty. If possible, try to tilt the tank with that corner down and fill with WO-40.
Spleify,
Either a router with template and pattern bit or hole saw should also be fine. If using a hole saw, use a 50:50 solution of Palmolive and water and do not stop the cutter in the kerf. Remove the saw often to clear chips and to slow heat build-up.
Personally, I'd use the router, much faster if you're comfy with them
James
I can't say with any degree of certainty but it *appears* kinda iffy IMO

That said, I've seen far worse hold for a long time so... hard to say with certainty. If possible, try to tilt the tank with that corner down and fill with WO-40.
Spleify,
Either a router with template and pattern bit or hole saw should also be fine. If using a hole saw, use a 50:50 solution of Palmolive and water and do not stop the cutter in the kerf. Remove the saw often to clear chips and to slow heat build-up.
Personally, I'd use the router, much faster if you're comfy with them

James