That's a great question! Dealing with those big, deep metal bins in cities or parks can be frustrating. The liners always seem to slip down. After a lot of trial and error, I've found one method that works consistently.
The key isn't just dropping the bag in. Start by fully opening the liner and draping it evenly over the entire rim of the can. Then, take the bag's drawstrings (if it has them) and tie them together in a simple knot over the rim's edge. This creates anchor points.
For bags without drawstrings, use a simple binder clip or a strong, reusable rubber band. Clip or loop it over a gathered section of the bag's top and onto the rim in at least two opposite spots. This provides tension and keeps the bag's opening wide and secure.
The goal is to use the rim itself as a fastener. This prevents the liner from collapsing into the can when heavy trash is tossed in. It makes removal easier too—just untie the knot or unclip, and the full bag lifts out cleanly. A quick wipe of the rim now and then keeps things sanitary. It's a small step that makes a big difference in maintenance.