Here's the update. I got a 50 qt blue rubbermaid cooler, which will allow me to do bigger beers without doing a parti gyle. A copper pipe fits through a sloping drain port without leaking. So far so good. Next I have to build a manifold for fly sparging.
The 10-gal orange cylindrical cooler will be retired. It may see use for insulating fermentation. The existing manifold will be used in an old 5-gal cylindrical cooler which will be used for the weakest beers, basically just Berliner Weiss.