Latex paint cannot be disposed of in the trash unless the cans have completely dried out.
There are several methods to dry out cans of latex paint, depending on how much time you have.
Small amounts of paint can be mixed with other colors or bulked together and used as a primer coat or on jobs where the final finish is not critical.
When you cannot use up or donate leftover paint, dry it out and dispose of it with your regular trash. All residual/leftover paint must be hardened or dried before putting in your trash.
Protect your work surface by lining it with old newspaper.
Simply remove the lid and place can in a safe, well-ventilated area.
Cans 1/4 or less full should dry in a few days.
Mulch, kitty litter, or shredded paper may be used as a bulking/drying agent. If you are in a hurry, buy some commercial paint hardener such as Waste Paint HardenerTM or a similar product to dry paint quickly. This is available at many paint and hardware stores. When mixed with paint as directed, it will dry even large amounts within a couple of days.
For larger quantities of paint: Pour thin layers (about 1" of paint) into a cardboard box lined with a plastic trash bag and allow the paint to dry one layer at a time. Adding an absorbent material such as mulch, shredded newspaper, sawdust or cat litter will help the process. Repeat the steps until all the paint is dry.
Donate unopened cans of paint. Schools, religious groups, community groups, and theater groups may accept unopened cans of paint, especially white paint. Even a neighbor may need some extra paint. Also, check your paint store's policy on returning unopened cans of paint.
In Waco, try the Habitat for Humanity Waco ReStore if you have unopened, usable latex paint. For information, give them a call at (254) 756-0131.