*Note 2: Metal cans usually rust before the paint gets old especially if they are stored in a basement where conditions are damp. The rust around the rim drops into the paint when it’s reopened, which discolors the product making it useless for touchups.
*Note 3: In most communities latex paint can be disposed in the trash provided it is treated such that the cans are lidless and the paint is not pourable. Generally, oil base paint is collected as hazardous waste.
Things you will need: old cans of latex paint, paint can opener or screwdriver, pliers for stuck lids, maybe a hammer claw or other sturdy puncturing tool to break into old stuck cans, plastic to protect floor or workbench, trash bags, kitty litter or paint hardener from hardware store, sturdy trash bags or contractor bags. Sometimes helpful: courage and a friend.
The process is quite easy, really. Set aside oil base paints for proper disposal as hazardous waste collection (check with your community). The way to know whether you have oil base paint is in the clean up instructions. If it can be cleaned up with soap and water it is not oil base. Let’s continue. Open each can of latex paint to determine whether it has solidified already. If so, the solid paint may be thrown away in the trash including the can but not the lid. Cans with liquid paint will need to be dried by one of three methods.
First, the can may be left open until it dries naturally (if you are in no rush).
Second, if the can is only about half full, inexpensive kitty litter may be added until the paint is no longer pourable. It may still be wet or moist but not pourable.
Third, a special paint hardener (available at hardware stores) may be added and stirred into nearly full cans of paint. Paint hardener takes up very little space and effectively treats a larger volume than kitty litter. It is extremely good at clumping paint together and continues to harden over time. Paint hardener may seem a little pricey for something that you’re just throwing away, but the end result justifies the cost.