Save the leftover paint.There's always something - picture frame, planter, basket, light switch, candleholder - that can use a touch-up or a touch of color.
Store leftover paint properly.First, clean the inside and outside of the rim with a clear rag. Replace the lid tightly by gently tapping it down with a rubber mallet. Store the can in a dry location, away from heat, cold, or source of flame, and out of the reach of children or pets.
Skin will form on paint that's left long enough.To avoid the mess of removing the skin, store the can upside down. When it's turned right side up, the skin will be at the bottom of the can. Be sure to use a rubber mallet to secure the lid tightly before turning the can upside down.
If you do want to get rid of excess paint, be environmentally friendly and check your community recycling rules for a facility that accepts hazardous waste.
