I have a 14 gallon rubber maid container that I use for my refugium. It overflows into a 10 gallon sump. I have a CPR overflow that can provide up to 600 gph to my sump and refugium. I then have a mag 5 pump in my sump that returns the water to the tank. I want a slow water flow through my refugium so I use a T fitting and a ball valve on my PVC pipe that comes from my CPR overflow. Most of the water goes directly to my sump while a trickle goes into my refugium and then overflows into the sump. As far as pump size, you just need a pump that has an output that is less the the output of your overflow, otherwise your pump will push more water than it receives and it will run dry.
