notching tank for external overflow

[mark]

re: drill glass with dremel, last hole I did was spd position 7 or 8 (out of 10) 1/8" round/ball bit, with 1/4" glass and about 7 linear inches and took ~ 20 minutes

Do you have the spreadsheet for slotted weir fr reefs.org? It's an Excel spreadsheet in their download section. You put in the number of openings and width and gives height and gph.