I've wondered the same thing about my 5 year old QP because in the beginning there were a few accidents and she poopeed on me. Then, I learned that she does that every 10 - 15 minutes, so I started timing her and putting her on her perch to do her business. I praised her when she did, and picked her up again.
One day she started nibbling my ear, then biting harder even though I said "gentle". Usually she minds the "gentle" command but not that time. I put her on her perch for "correction", where she immediately pooped. Now I know that she was getting desperate because her hints were being ignored.
Just be attentive and time your parrot for an hour to determine the approximate interval between poops. Once you have the "timing" figured out, put him/her on your shoulder and put him/her on the perch, praise a lot when the poop happens, "Good girl, poopie!!" take her back on your shoulder and repeat several times. Then, watch for a hint when the next expected poop should happen. He/She will let you know, but you have to identify the hint he gives you.... and never ignore it.
I have to back up a bit though. I did the timing/putting on perch for poops for a couple of weeks, religiously. The day she started biting I was engrossed in a book and didn't think anything of the nibble until it hurt. I think it took Clover training ME, not the other way around!
