There are restrooms and showers at the cabin pool. It's around the 2500/2700 loops, if I remember right. We haven't been there since that pool was refurbed this winter/spring, but I can't imagine they removed the restroom facilities.
I also used the laundry in the 1100 loop CS on our last trip when we had a cabin in the 2100 loop. It was a short walk, but not something I'd want to do if I really had to pee.
You can put in a special request of "2500/2700 loop, Close to pool" if you call directly. That might give you the best shot. But if you do end up in 2100, the cabins all the way around at the end of the loop will be closest to the comfort station.