That is the flush actuator (you press the buttons to flush toilet with dual flush for water savings) and it is removable to access the toilet tank. I have been working with these for 10 years plus, and this is one of the most under utilized products on the plumbing market IMHO... email sales@poshhaus.com if you have any questions about how the wall mount toilets work....

http://www.poshhaus.com/store/c/24-Toilets.html

Thanks for the info; I was considering wall mount toilets for our new build, but was unsure about how repairs would be carried out with the tank behind the wall.