Refugium help

I have been racking my brain for the last couple days trying to figure out a refugium. Im using a 40 gallon breeder for a sump and didnt have any room for a refugium. I have a 10 gallon spare tank not being used for anything and want to use it. There is a little spare room in my cabinet for the 10 gallon. My question is how to het water from the sump to the refugium then back to the sump. Would like to keep everything hidden under the cabinet. im thinking just a couple small pumps, but if one fails it could be a big flood. My other thought was to drill both the refugium and sump, use a couple bulk heads and let the water pump in the refugium and overflow back into the sump. Anyone else have any ideas?

 

Just T your return line into the 10G sump and drill the sump and gravity feed it into the fuge

 

How big of a fuge do I really need? I could do a 5 gallon and build a stand for it so it is above the sump a hair and drill it with a bulk. Then it would gravity drain back into the sump. Afraid a 5 gallon is a little small for a 150 gallon tank.