First, you have too many steps between ringing the bells and going out to potty. Dogs have more short term memory...ring bell, go right outside to potty. Yours is ring bells, go to hall, sit, go outside.
Second, not all dogs learn to associate telling that they have to go outside. I've had everything from waiting on a mat at the back door to stand and urinate where ever the mood strikes me. With three dogs in the house, we now find that feeding on a schedule 2x/day, letting them out and hour after each meal, first thing in the morning, our lunchtime if someone is home and they are not crated, and last thin before going to bed works best. Everyone has accommodated to the schedule. And schedule what goes in so you can schedule what comes out and when.
Second, not all dogs learn to associate telling that they have to go outside. I've had everything from waiting on a mat at the back door to stand and urinate where ever the mood strikes me. With three dogs in the house, we now find that feeding on a schedule 2x/day, letting them out and hour after each meal, first thing in the morning, our lunchtime if someone is home and they are not crated, and last thin before going to bed works best. Everyone has accommodated to the schedule. And schedule what goes in so you can schedule what comes out and when.