The Flying J dump stations were free for years but that changed about the time of the Pilot merger/buyout.
Flying J is nothing like it was when Jay Call owned it before he died in a plane crash,they started in the 60's catering to the RV people free water,dump,discounts on fuel it was nice. .Now you have 2 different outfits owning F/J and I don't stop period at a F/J owned by Pilot
Anyway, I don't like overnighting in truck stops because of the noise of trucks coming and going. I like to find a nice quiet side street in a commercial district instead. However, you can't get away with that in many areas of CA because that is what fulltimers/homeless are doing and the local police do night time raids. A lot of these fulltimers are employed but can't afford the outragous rents for a home or even an apartment.