Thanks for posting info/pics. Sorry, I've been short on time.
Is one of your overflows drilled holes a straight shot to the desireed sump chamber? If, so maybe that could be your trickle line? Just worried it might get loud with a multi-directional path.
Could you run a full siphon,(throttled with gates), in each overflow? Then you would have 50/50 surface skimming. The 3rd remaining hole closed to sump chamber could be trickle line that converts to full siphon in an emergency. 4th and final hole would be slightly higher emergency standpipe.
Im no tank wizard and have never delt with tank and flow rates as big as yours...
Have tried posting on bean animal thread on RC? a lot of experience there especially with larger set ups
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