In order to get Chicken and Boljak to pee and poop in bathroom, I would give them their favorite treat after they had successfully done so.  Eventually, the two of them caught on and they would take turns peeing and pooping.  This way they both get treats 4 times each.  At some point, Chicken maybe thought it was the act of going inside the bathroom that was getting rewarded.  She went inside with me one morning, and after washing my face, I saw her outside the bathroom door doing her happy dance. Nothing on her doggy pad, but this little thing was happily anticipating a treat.