Tired of your paint and varnish cans crusting over on the inside? This happens because changing temperatures can loosen the lid.
First seal the lid by tapping with a hammer. Slight imperfections can be overcome by putting a thin bladed screw driver in the slot and seating the lid firmly. After firmly sealing the lid, store the cans upside down. No air will possibly leak by a liquid seal.
If you’re not sure of the seal start by storing the can the first night on a flat cafeteria tray or something similar to catch any errant leaks.
Storing the containers upside down also works well with PVC pipe glues.
– Gary A. Gorsich