Potty training a grey

I have to admit, my parrot would've received a bit more attention had it not be for his poor potty training...

so what method can i use to teach him to behave himself while not at his cage?

Not sure if my method of potty training was correct but I'd take him out of his cage and tell him "no pooping". Pooping on his way to his perch (which has a tray with paper) got him no praise and a disappointed "no pooping". Pooping when he got to the perch, lots of praise. Eventually, he learned to hold it (or try to) until he got to the perch. Then I worked on "now you can poop". As I set him on his perch I'd say "now you can poop" and, as trained, he would. Now he understands that when I say that he can poop. His reliability is spotty but he tries.

with my conure, when I first got him, I would let him be on me, then after a few min. set him on his perch, when he went to the bathroom I would pick him back up, he learned that way to go on the perch, downfall??? now he wont go to the bathroom in his cage either, only when he is on a perch of some kind, be it his stand or a rope.