The author of the Diorama's FAQ book Rubén González has produced an excellent how-to-use video on AK Interactive’s Washable Agent.
AKI-WA-236 Washable Agent
AK Interactive is back with another innovative product which converts any acrylic paint into a washable effect. Just add a 10% of this product to your acrylic paint to make it washable. Once the mix is applied you can remove the desired quantity with a brush moistened in water. This product is recommended for winter camouflages, to create any dust effects, or to imitate the faded quality of paint on vehicles, for example in the desert where the paint underneath was faded little by little. The result is very convincing as it is based on the same principle as the real paint. Since it works with all acrylic paints the possibilities are as endless as the colors available.