Great  question! Our back to wall units are bowls that sit on the floor, but still have an in-wall tank system. The weight of the person is supported by the floor, as opposed to being suspended like a wall hung. Our back to wall units use a different in-wall tank than our wall hung units, they are not interchangeable. You can learn more about our Wall-Hung units here!Wall hung units use a tank inside of the wall that has a supportive metal structure. This structure is bolted into the studs and is what supports the weight of the bowl and the person using the unit.