that makes no sense...
your iwaki for the skimmer doesnt or shouldnt have anything to do with your iwaki return pump,
what benifit would there possibly be by trying to plumb them in together??
i was trying not to drill another hole in my sump. and a tad cheaper. trying to figure out how to plumb it. i thought of adding a t to the bulkhead and one side to my return the other to my skimmer. i didnt know if the 1" would be to small to handle that kind of pull.