Tbh due the training before hand and his comment on not eating solid foods I dont think he actually went to to bathroom. I think its just whatever was in the syringe.
If there was something like that in there i dont think he wouldve wanted to drink what was in the pot because i think he was with her on never wanting to explore that even b4 he meet her and hes such a good submissive that if that wasnt the case b4, once she expressed her very intense desire NOT to do anything involving that he completely let go of any curiosity he couldve had about it.
If you look at when he put it away, it was covered. It has a cap on it exactly for that, though I'm pretty sure we can assume there was no actual poop from what they've said during the buildup and this chapter.
does the uncovered poop in a bowl not stink i feel like they shouldve covered that