make one of the tanks higher than the other maybe a couple of inches then drill one of the sides put a bulkhead in little bit of pvc maybe a 90* elbow then let gravity do the work after that or tee off of your return to drain into the higher one then have that one drain back into the one with the return pump. i have my sump with the return then an 18tall that is feed by a tee on my return so i can slow the flow down for the refugium part wish i had a camera. hmm if you see the pictures youll understand why i need a camera but it get the point across i hope
