Overflow dimensions

[mark]

The advantage of 2 overflows is you have a back up in-case on gets blocked. How likely that might happen considering you can guard with screens etc. There's also that the flow is split between two so quieter. Disadvantage is you have another overflow taking up space.

My understanding is RC calculator is for a linear weir (no teeth), so 9 inches isn't that much. It's going to be more how much footprint you need for the bulkheads, if glass tank allowance for drilling close to edges, room to get you hand in. Can also consider just going at a diagonal. I've got 2" drains so my dimensions not much help but sure someone with your sizes will post. You don't need teeth btw.

Have you thought about other types of overflows such as external, horizontal in tank, linear pipe? Standpipes other than Durso eg Herbie?

[mark]

Thinking about this on the drive in from work.

Consider a single 12" diagonal overflow in the corner with 3-1" bulkheads. Laid it out on paper but since at work don't have a 1" bulkhead in front me so guessing on footprint for nut and flange so might be able to go smaller. The bulkheads would be drilled 2 on the diagonal face, 1 in the back corner. 2 of the bulkheads, vertical standpipes for Herbies (primary and emergency) third bulkhead for return.

With this the 1" return allows less restriction, the Herbie give a silent overflow with a backup drain.

[mr_alberta]

There is no way you could run an external overflow (and I don't mean an external overflow box like a cpr)? The next time I build a tank, that's what I would do. That way you maximize the area inside your tank.