Overflow Box ISSUES - HELP ME PLEASE

[Peter McFarlane]

hey guys i have two tanks that im looking to set up as below with one massive filter holding enough media for both.

i was planning to drill the tanks (as in the diagram), but i'd prefer to use an overflow box instead. i'm very confused about flow rate.

i was thinking of using an overflow box similar to the one below. but cos my big external filter wasnt meant for this sort of setup, how can i gauge the flow rate?

any help would be much appreciated.

 

[Mattyou]

1" tube is rated at around 600 gph, depending on the number of overflows and the size of the tanks your plan will work. I need more details to be better help though.