Tasha is a puppy mill rescue. She was used to peeing and sitting in it. Learning house rules has been a challenge for her. We are about 80% there, after 10 months.

Find a high value treat; something the dog goes NUTS for. With my Tasha, that is bits of hot dog. When the dog goes outdoors, praise, praise PRAISE! I jump and down, wave my hands, GOOD JOB, GOOD GIRL, the neighbors must think I am nuts. And Tasha gets a bit of hot dog. After about 3 weeks, I didn't have to keep the hot dog with me in a baggie in my pocket any more; she knew we would run in to the fridge for me to break off a bit for her.

When she goes in the house, at least initially, you ignore the dog. Make noises of disgust, clean up, don't approach the dog.

When the dog goes in the house, it is key to clean up and eliminate the smell. Dogs will go in the same place as the smell tells them this is a pee place. Maybe put a pee pad there, let the dog use that and move the pad closer and closer to the door, then outside. While I haven't done this, many folks on the bichon forum have had success in this way. (I can't use pee pads, the cats think it is a new toy to shred. And if there are dog poops on there, those roll! )

I've taught Tasha a lot of commands, and we've moved to lower value treats for most of them. But the house training? Still using those high value treats to keep her attention.

Hope this helps!