To clean my RCs I use a compressor turned up to 70ish PSI and blow the dirt off. But I don't drive mine in mud / water.
For the manual, I couldn't find one for your specific model on the Traxxas website. So I looked up one for a similar model that should have all of the same features, just a different body and maybe a different wheelbase:
TRX-4 1979 Chevrolet Blazer
traxxas.com
The support section of that page should give you access to a .pdf version of a manual which should be close enough to your model to get you up and running.