Was it absolutely necessary to remove the old drain once you had access?
My cooler drain line now ends at the inboard side of the cooler after being nicely cut up removing the sole. I have been inclined to leave that stub and just let it drain into the bilge over the epoxy that I have glassed in. I like your solution with the Y-valve, but I don't want to make or expand my projects right now. So unless it was really easy I would postpone this fix for another day. But it would be much easier to do this fix now while everything is exposed.
Fortunately it is not that hard to keep beer cold in the Great Northwest, so getting really aggressive with cooler fixes is one of the advantages of our climate. Now if you want to talk about rust and corrosion and moss, that is a whole other thing.
