Steps to make a disposable paint tray liner using a plastic grocery store bag.
1. Get a plastic grocery bag that doesn't have any holes in it.
2. Open the bag and slip it over the paint tray.
3. Flatten the bag over the tray so that it covers the entire interior of the paint tray where you will pour the paint.
4. Pour your paint in the tray.
5. Once you are done painting, let the paint dry on the bag.
6. Remove the bag and repeat the process the next time you paint.