heres mine. https://forums.saltwaterfish.com/t/371549/55-gallon-sump-setup
the overflow comes in from the top left. the frist chamber on the fer left of the pic just has the heater and the skimmer in it. small waterfall down to the refugium level. Put cheato, live sand (or miricale mud) and some live rocks in thsi section. In the pic I have it loaded with live rocks. that was kind of a holdinga rea until i put those rocks in the DT. not like that anymore. and then the far right chanmer has nothing in it but nice clean water for the return pump to pump back up to the display tank. I have a valve on the return side going up so I can adjust the water flow of the pump as it slightly overpowers my overflow.
I also have a valve on the overflow side, but this gets kept wide open. its only there for serious maintenanceor some sort of disaster.
Just make sure that wehn you are done you have enough room (in case your return pump goes out) in your sump to hold the extra water that will drain down until its past the teeth on your overflow box on the inside of your tank.
Basically the only thing that can go wrong (murphys law ) is that somehow your overflow could get plugged up or lose siphon and then you would end up with whatever water you have in the far right tank would fill up your display tank until it overflowed (unless you keep it really low in both area)
I'll post a pic of the actual plumbing in a sec
Hope this helps