Use a can of latex or oil paint once and the rim invariably get coated with dried, crusty paint. This solution is unusual and counterintuitive, but it really works.
By the DIY experts of The Family Handyman Magazine
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How to Store Paint: Keep rims clean
Puncture and drain
Use a small nail to drive four holes in the rim of the paint can. Let the paint drain back into the can and seal the lid with a block of wood and a hammer.
With the lid tightly sealed, flip the can upside down for storage.
We’ve covered paint can storage tips a hundred times before. But this tip comes to us from a house painter with thousands of paint jobs under his belt. Rather than spending time trying to sop all the paint out of the rim, he punches four small holes in the valleys and lets it drain as shown. Then he stores the cans upside down. He swears it works like a charm.