Im new to this but had a thought. What if you have his litter box outside when you take him out to gradually get him used to going outside of the house. Once he gets that, you can try taking the litter box back in.
Also everytime you take him out tell him to "go potty" (or whatever you want to say) and when he does tell him "good boy! Good go potty!". After a while he will figure out what go potty means and will do it when you tell him to.
My puppy will squat even if she doesn't have to go whan I tell her to go potty and I've only had her a week.
Just some thoughts!
