Soap and water WILL strip off the paint!
Alot of people here talk about that too, but don't listen! If you washed the part before you applied the paint, just make sure the painted surface is dust free and smooth feeling. If you're still nervous, just lightly wipe the model with a dry, soft rag. Then, brush your future on, and everything will be just fine! I've never washed before applying future, and have yet to have a problem with adhesion!