I wish I could take credit for this idea, but I actually came across it on a blog some months back (can't remember which one, or else I'd link back to it.) I finally put it to the test this past weekend, and I'm not looking back. All you need, besides your prepared piping bag and frosting, is plastic wrap (aka cling film, Saran Wrap, or in my case, "Kirkland Stretch-tite".)
Start by laying down a length of plastic wrap. Plop down some of that frosting on it, closer to one edge (i.e. not right in the middle.)
If you need a lot of frosting, this technique will allow you to fill the bag with more than you would ordinarily. As you will soon see, the excess will not squirt out the top. More frosting in the bag = fewer stops to refill.
Step 2: Wrap the frosting in your plastic wrap, into a roll that will fit comfortably inside your piping bag.
Next, twist the end of the plastic wrap that's longer, nice and tight, like so:
Now simply feed your roll of frosting into your piping bag with the open end going in first. You see where I'm going with this.
Squeeze the back end of your frosting roll so the frosting breaks out into the piping bag.
Now you can start piping as usual, without having to wash your greasy hands from filling your bag the old way! Also, as I mentioned earlier, there's less risk of frosting squishing out the top of the bag because you twisted the plastic roll shut. Good, right?
But wait! There's more!
Check out how easy it is to clean up when you're done:
Just pull out your plastic roll and discard. And if that wasn't enough, my piping bag was in much better shape to reuse, which means less waste, which means happy Gitu.
I bet this technique would make "striping" a breeze (I may have just made that term up, but I'm referring to the technique where you fill your bag with 2 colors of frosting.) Ooh I might try doing 3 or 4 now that I have this handy trick up my sleeve.
Oh, final step: Get a manicure already.