Actually, I had a roo years ago that was literally potty trained. It is possible. He taught himself.
Me and my family (I was about 14) went on vacation and left him with my grandparents. Well...they had a half bath they left him in, loose, and left the lid up. He ended up falling in, and I guess he started perching on the rim of the toilet...? Anyway, by the time I got back, when I would get him out, he'd run around and when he had to go, he'd hop up, do his business, then jump back down again. If I was carrying him, he'd start doing this growly cry and I'd take him in the bathroom. It was amazing. I never talked my parents into letting him run loose in the house, though.
If he was near the bathroom, he'd go in himself. If we were in another part of the house, or somewhere he wasn't familiar with, he'd cry.
This was a bantam barred cochin. He was really a great bird.
Shelly