I have never had a rectal exam from my gi (Thank G-d). expect to tell your story and be asked a lot of questions. bring any and all paperwork you have. be weighted and blood pressure and if they do blood test there that to go with the urine sample. all the usual fun.
my gi physical exam is lying down with my belly uncovered and he listens to it with a stethoscope, tapping on it, and pressing all over. Good luck!