My daughter (who is 22 now) was 16 months old, and started sneaking into MY bedroom, beside the bed-taking her diaper off , and pooping in the FLOOR!
after a couple days, i got the potty chair out and put it in that spot. guess what? she started using the potty-for everything at once! then i moved the potty to the bathroom, and that was it for her. she did it herself. BOYS were another story!