At MK the bathrooms next to cheshire cafe are almost always empty. I also think the bathrooms in the dumbo area near casey’s splash pad are good.
At HS, the bathrooms near the entrance of TSL - past one man’s dream and right next to the Joffrey’s stand. These are our favorite because there are plenty of benches outside for a meeting place for split party and everyone is usually trekking into TSL and doesnt stop here.
AK - there are bathrooms next to the Nemo show that basically have no one using them right now since the show is not running.