Acrylic paint is thinned (or reduced) with water, alcohol, or its proprietary thinner. In the case of Tamiya, thinning should be done with either 90 percent isopropyl alcohol or Tamiya thinner.
Tamiya, and most other acrylic paints, can be cleaned with either Windex or Simple Green or detergent and water.
Never use paint thinner, or any organic solvent other than alcohol, to clean brushes used with acrylic paint. Organic solvents are essentially incompatible with the binders and pigments in acrylic paint. In fact, it is highly recommended that you use different brushes for acrylic and enamel paints. (The brushes will last longer.)
Tamiya paints have a tendency to "flash dry" when brushed. For large applications, use an acrylic retarder. For small applications, dip the brush in 90 percent isopropyl alcohol or Tamiya thinner before dipping it in the paint.