Leftover latex paint is one of the hardest items to recycle; many paint-recycling programs have been suspended since water-based paints are not considered a household hazardous waste. But that doesn't make it safe to pour paint down the drain or put half-empty cans in the trash (which is still illegal in most communities). Instead, all you have to do is let it dry out. Mix in something called "paint hardener," which you can find at any hardware store. It will take a few hours to dry out and harden; toss the disc of paint into the trash and the empty paint cans can go right into the recycling bin.