I am currently remodeling my girlfriend's 1st floor bath. There is a wall between the kitchen and bath that houses all of the home's waste and supply lines. We had a plumber come in and cut everything out and replace it with PVC and PEX. While this wall is open, I was thinking it's worth considering running plumbing to the attic, which is huge, in case we want to add a bath up there in the future. My question is what would have to be done for waste pipes on the second floor? Can the main stack in the attic be tapped into? Does it have to be split in the crawl space? Basically, it would be simple to run supply lines up there but I'm not sure how involved the waste lines would be. I don't want it ready for a bathroom, I just want to be in a position where a full bath can be added without having to rip up anything on the first floor. I've attached a picture to help make sense of my question.