What return line? From the top off container to the tank or sump? If so plumb it any way that looks good.
I have a 25 gal
container that has my top of water in it. There is a pump inside that has some vinyl tubing that runs into a section of the sump. When the float is low it triggers the pump to put water in the sump.
Having a sump makes this easier but it could be done in the tank as well. Looks are more important there.
Any specific questions? What type of setup do you have?
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,