Acrylic paint is water-based, and it washes away from a paint brush easily with soap and water -- if it's cleaned before the paint has a chance to completely dry. If the acrylic paint dries completely, you can still salvage the brush and restore its former condition using a homemade solution. For hard, dried paint that's tough to remove, use water-based solvents on the paint brushes. They'll soften and break down the paint, resulting in a clean paint brush.
Fill a container with hot water and 2 tsp dish soap.
Lay the brushes down in the container so that they're completely submerged in the soapy water. Allow them to soak until the paint softens.
Press the brushes into the edges of the container to squeeze out the paint. If the paint isn't softening, empty the solution and add more soap and hot water, and repeat the process.
Rinse the brushes with warm water and allow them to air dry.
Fill a clean metal container with acetone or denatured alcohol.
Place the brushes into the container until the paint softens.
Run a thin, pointed object through the bristles to separate them and loosen the paint. Soak the brushes in the solution, and separate the brushes until all of the paint is gone.
Rinse the brushes with warm water. Wash them with dish soap and rinse them thoroughly.
Smooth out the bristles and lay the brushes flat to air dry them.
Don't put acetone or denatured alcohol into a plastic container.