Cole004 90 gal reef

[mark]

few things,
-first your first drawing, looks like the overflow goes into you reservoir then to the sump and still see on your plumbing, still does with a valve, wondering why
-doesn't appear you have an overflow box just a straight standipe, again with a valve. Can understand the valve to backup the flow over the standpipe for noise (Herbie) would just caution running without a backup or emergency drain
-in the drawing you refer to a CL, technical correct as is closed but usually referred as a return manifold. CL for aquariums seems to be more the drain and return at the same head.