W.M.
our son was peeing in the potty perfectly about 4 months before he would poop in it. He wore underwear, but would either poop at nap or bedtime when he was in a diaper, or just hold it in. After he would go 6 days without pooping, we told him he could bring us a diaper to put on him when he needed to poop. We always encouraged him to go in the potty and finally one day he decided he didn't need the diaper to poop in, so he started using the potty and no poop accidents after that. He'll do it in his own time. The occasional diaper beats cleaning out the underwear! Good luck!