Pastry bags are an indispensable tool when it comes to neatly piping cupcake fillings , frosting , icing , and even pate à choux pastry treats like gougères . That is, if you know a few simple steps that'll transform filling a pastry bag from a messy endeavor to an easy task that requires little cleanup.
To get started, you'll need a pastry bag  — a large resealable plastic bag with a corner snipped off works in a pinch — a pastry tip (if using), and a pint glass.
- First, if you're working with a pastry tip, nestle it into place. If you're not, or if you're using a disposable or reusable bag, don't bother snipping off the tip of the bag just yet; that'll come later.
- Place the pastry bag in the pint glass, pushing the bag's tip down until it hits the bottom of the glass, then fold the top of the bag over the rim of the glass. This way you'll have some wiggle room between the filling and the top of the bag, which makes it far less likely for the filling to overflow when in use.
- Load the bag to the brim of the glass with your filling, and then unfold the bag and twist it until it's taut and no air bubbles remain. If working without a pastry tip, snip off the tip of the bag and get to work piping!
Bonus: the pint glass makes for a great resting place for the filled bag when not in use.