My SIL used to live in an old tenanent apartment with a tub in the middle of the kitchen. I think it had a curtain. My kitchen in Manhattan has a large closet in the kitchen with a toilet. No other facilities, but the closet was next to the kitchen sink, so you could wash your hands there. It also had a lot of high shelves, so we used it for all the stuff we didn’t want the kids to be able to reach. It was the second toilet in the apartment, and super useful.