Well, how do we know he doesn't use dialysis and have a colostomy? I mean he was nearly burnt to a crisp, so I imagine a few 'appendages' and orifices might have been charred beyond recognition.
Hell, do we know if he can even eat anything or is it all IV?
It is canonical that he does not poop or pee outside his suit. His suit handles all of his evacutory responses. He does not eat, a nutritional paste is injected directly into his stomach because his esophagus is virtually destroyed. It arguably received the worst damage from the fire.
I bet they've upgraded so instead of ostomies they have cybernetic poop compactors that shoot out little compressed bricks, easy for use in imperial construction.