While dish soap is not the most ideal product to remove tar from a car, in a pinch, it can be used. It is important to use a dish soap that is grease-cutting and has active ingredients like sulfates. Apply the dish soap to the tar spot on your car with a damp cloth. Gently rub the area until you see the tar start to break down. Once the tar has been removed, rinse the area with water and dry it off.