M.R.
I started PT my son at 3.5 and he too refused to poop in the potty. It was frusterating (he did it once or twice in the beginning and then refused). This went on for 5, maybe six weeks (I was giving him time) and many soiled underpants! By the sixth week, I looked for cues of he was about to go poop and I sat him down on the potty, kicking and screaming. I held him and held him down and told him it was not bad. He pooped while he cried and smiled at the same time and then said, "See mom, it wasn't bad." It took 2 times of me doing this. By the third time, he said, "Mom, I have to go poop" and he sat on the potty and went. No more poop accidents. It's now been about 8 months.