Tips on housebreaking a 7mo

Wilbur is a 7 month old basset and I adopted him 4 days ago from a young couple off Craigslist. I’ve been wanting a basset for years now, and am in a good place to adopt.

I have so much patience and empathy for him, but his previous owners didn’t work on his potty training. He’s never pooped inside- we go out several times a day for walks and he has a backyard. I’m in a 750 sq ft duplex.

He pees inside a few times a day. I always let him outside and reward him once he potty’s and comes back up to the porch with a treat and “good potty outside”

I want him to succeed- so any tips help!