??
not sure what the return pump has to do with your skimmer... (nothing)
for a dual injector etss, you need at least 1200gph of high pressure flow through that thing,
i would actually use like a 1500gph pump, which would be the iwaki 70rlt.
from there you can plumb the outlet of the skimmer to your refugium,
but no way you can use your overflow to power this skimmer period.