That's a great question! A floppy bag that slips into a round bin is a common frustration. The "best" method often depends on your specific bin and needs, but here are the most effective and natural solutions people use.
For a simple, low-cost fix, try the Bungee Cord or Shock Cord Loop. Stretch a loop around the outer top rim of the bin, then hook the bag's lip under the cord at several points. This creates even pressure that holds the bag snugly against the inner wall. It's adjustable and works on most round bins.
Another popular trick is using Large Plastic Spring Clips (like binder clips or heavy-duty bag clips). Simply clip the bag's top edge to the bin's rim at 3-4 evenly spaced points. This is incredibly straightforward and makes removing the full bag easy—just unclip.
If you want a semi-permanent solution, consider Adhesive Hooks or Clips. Stick 3-4 small, sturdy hooks around the inner top rim of the *clean, dry* bin. Loop the bag's drawstring or top edge over these hooks. Be sure the adhesive is rated for outdoor/plastic use.
For bins without a pronounced lip, the Double-Sided Tape or Velcro Strips method can work. Apply outdoor-rated tape or hook-and-loop strips horizontally just below the rim inside the bin and press the bag against them. The hold is good, though tape may need occasional replacing.
Finally, the simplest approach is to Use a Proper-Sized, Thick Bag. A tall, heavy-duty bag designed for round cans often has a wider top that fits snugly. Sometimes, the right liner is the only hack you need.
My personal favorite is the bungee cord method—it's versatile, cheap, and works on almost any round can. Give it a try first!