If you want to understand the role of the sweeper and more important, his usefulness in a tactic, you have to go way back in the 80's and 90's when this role was very popular. It was originally ment to substitute the today's defensive miedfileder, allowing CD's to push a little higher on the pitch. You can find lots of information about the Sweeper and Liber, how it appeared and how it slowly dissapeared in modern football. Once you understand these reasons you will be perfectly capable to integrate this role in basicaly any kind of formation with the required implementation. I can offer more info about this but im not sure if I am allowed to post links to external websites here. You can contact me on PM if you are interested. Personally, I am a big fan of this role and I desperatly tried to implement it in whatever formation I possibly could.