I found this tip on another blog recently and it has changed the way I handle icing! There is no longer a need to clean piping bags! All you need is cling wrap!
Start off by tearing off a square of cling wrap and laying it out on a clean surface. Then place the icing you plan to use in the middle of the square.
Fold the cling wrap diagonally in half. (Corner to corner)
Next, roll the cling wrap around the icing in the middle (like a piece of candy).
Then twist the ends until tight.
Then slide one end of the cling wrap through the coupler in a piping bag.
Cut off the plastic wrap poking out of the coupler.
Then put on your tip, the other half of the coupler, and start piping!
Once you are done and all of the icing is gone, simply remove the top part of the coupler and the piping tip. Then pull the cling wrap with the residual icing out of the bigger end of the piping bag! You will most likely have to clean the bottom part of the coupler, but that is so much better than having to clean out the piping bag as well!!
I found this genius tip on the following blog: http://www.sweetsugarbelle.com/2011/03/coloring-and-preparing-royal-icing/