My plan with the double rubbermaids was:
#1 economize on space.
I wanted to have a refugium and a frag rack, but did not want to get macro growing in with frags.
#2 Slow the flow to the downstairs and collect some of the bubbles
With the first tank, I'm able to get the 3 feeds from the tanks upstairs falling to the same place, and the bubbles hit there and disappate. The macro will go up there and should get some good water flow over it.
The bottom tank I have the drain situated to the back, and not much air is falling down there at all.
The bottom rubbermaid is plumbed with 2 x 2" lines to an acrylic 90 gallon sump horizontally. So when the power goes out, and the system drains back, I have an extra 120 gallons of capacity, as the sump runs half full currently.