Does the motor turn over when the pull start gets hard to pull? If so, the engines probably just flooded.. Pull the glow plug and turn the car upside down to let the excess fuel run out, then pull the starter a few times to clear it out, reinstall plug and try again..

As for cleaning nitro cars, you can get "nitro cleaner", but it's not cheap, and probably just some fancy "simple green" or similar.. I use water sparingly on mine, being careful not to soak the carb or aircleaner, and trying my best to dry off the car afterwards. Compresed air is the best thing to use.. I use my compressor and blow off all the loose dirt or excess water.. Once done a few well placed squirts of WD-40can help disipate remaining moisture.. Also try not to soak any ball-bearings or electronics as well, cause stuff will rust and short circuit if it's gets wet.. Just use common sence and dont go overboard with the garden hose, and you should be ok!