"Around": After the thrower looks dump, the mark shades around, giving the up-the-line throw more. The player on the reset only gives his marker the throw backwards. The player on the sideline is talking to the defense.
The drill rotates pretty organically. Watcher becomes thrower, thrower becomes mark, mark becomes dump mark, dump mark becomes dump, dump becomes watcher.
"Back": Upon engaging the dump, the mark now shades more straight up, forcing the thrower backwards. The dump mark forces the dump to cut up the line. The rotation is the same as "Around".