Wondering how long you can keep opened cans of paint, and how to get rid of them? It's a tough question. The truth is that if paint is kept sealed and in a cool area that won’t freeze, it can really last indefinitely.
The best way to preserve your paint is to make sure you do a good job wiping the lip of the can before resealing it.
One way to keep paint from building up in this area is to add drain holes when you first open the can. You can easily create these using a sharp screwdriver and hammer to pierce the inside of the lip of the can.
As far as disposal goes, regulations for disposal of paint in liquid form vary from town to town. However, one option is to just leave the cans open until the paint gets hard. Adding kitty liter into the leftover paint will help it to dry the more quickly and allow you to dispose of it much more quickly, too. Unless local government regulations tell you otherwise, toss the cans out with your regular trash.