Use a carabiner to attach the loop to one of the anchors. This loop is called a safety loop, and it should be slack.
Tie a clove hitch around the spine of a carabiner so that the carabiner keeps the rope from pulling through the rapide.
Have everyone but the last person rappel.
The last person should verify that the clove hitch did not slip and that the safety loop is still slack.
Attach your rappel device to the rappelling strand of the rope.
Unclip the safety loop from the anchor.
If you're comfortable that the biner block will not slip or pull through the rapide, you can put the carabiner away. Otherwise, clip the carabiner to the pull strand of the rope. Be advised that this makes the retrieval slightly more difficult.
Attach the pull cord to the end of the rappelling rope (on the non-rappelling side).
Toss the pull cord to the bottom.
As you rappel, verify that the pull cord reaches all the way to the ground.
At the bottom, untie the stopper knot then pull on the pull cord to retrieve your rope.