Agree with Al that you seem to have dodged a major bullet! Did you ever see the movie RV with Robin Williams, Jeff Daniels and Kristin Chenoweth? Al's advice is also good to follow IMO.
Yes, the black water flush system has an anti-siphon valve which probably prevented your city water and plumbing system from getting polluted. I would still fill the fresh water tank with good clean city water (using a whole-house type filter inline to make sure the water has no particulates going into the tank), and add bleach per other threads to sanitize the tank, and run this water through all of your plumbing lines (hot and cold).
This will be easier to do while hooked up to a sewer connection. Just run the pump water/bleach from the tank through all lines and let it fill the grey tank, and part of the black tank via the toilet flush. Then dump the grey tank, close the grey valve, and dump the black tank, and close its valve when done.
Open the grey dump valve again, and run city water from the [ correct
] sidewall connection, and run all kinds of (filtered) city water through all the plumbing lines many times to get the bleach residue out.
Maybe overkill, but your health is paramount . . .
PS -- PS -- sorry but I keep having to chuckle at the whole event . . .