That's a great question, and a common frustration in urban kitchens where tall, slim trash cans are a space-saving necessity. The best way to secure the liners really depends on your specific can and how much effort you want to put in. Here are the most effective methods, from quick fixes to more permanent solutions.
First, the simplest trick is to ensure you're using the right size bag. A bag that's too small will never stay up. If your bag is the correct size but still slips, try this: after placing the liner, pull the top edge of the bag over the rim of the can and secure it with a simple, large rubber band or a small bungee cord looped around the outside. This creates downward pressure that holds everything in place.
For a slightly more discreet solution, consider using adhesive hooks. Apply two or three small, plastic adhesive hooks to the *inside* of the trash can, just below the rim. Then, you can hook the bag's drawstring or its top hem onto these hooks. This method is very effective and keeps the bag neatly out of sight.
Another popular hack involves double-sided tape. Applying a strip of strong, waterproof double-sided tape around the outer rim of the can will grip the bag firmly. Be sure the surface is clean and dry for the best hold.
If you're dealing with a particularly slick or narrow can, sometimes the best approach is a physical barrier. You can place an empty toilet paper or paper towel tube vertically inside the can before putting the bag in. This creates just enough friction to keep the bag from collapsing inward and sliding down.
Ultimately, the most reliable method is often the rubber band or adhesive hook approach. They are inexpensive, easy to implement, and solve the problem without much fuss, keeping your urban kitchen tidy and functional.