Overflow dimensions

[mark]

WuHT not to turn your post into a how much flow to my sump thread but you mentioned 600gph. If that's what you want, then your on the edge of seems accepted a 1" inch bulkhead will gravity flow.

Before can say more, what type of tank you planning, what type of turn over and how much you planning on relying on your return pump for display turn over? One leaning is flow no more to the sump that the gph rating of the skimmer, I at one time had 2000gph going through my sump (since reduced to 1000gph).

Me, I'm on the side of go big. Just because you have a big hole doesn't mean you have to max it, but does allow for flexibility as plans change. Applies to return bulkheads as well as drains, Realize overkill but I have 2-2" drains on a 145g.