The entire toilet tank is flush against the wall with a back-to-wall type of toilet. The rear of the cistern sits above the toilet pan, and the entire unit is flush against the wall in this case. Unlike a close coupled toilet, there is no space or gap between the toilet and the wall.
A back-to-wall toilet is a one-piece unit that boasts a sleek, modern appearance. Because there are no tight gaps behind the toilet's rear, they are very simple to keep clean and all of the piping is concealed. They're also easy to maintain since the reservoir can be readily accessed if there's an issue with it.