Can anybody give a tip how to fill your RV tank from a drinking fountain at the state parks camgrounds where there is no water hook ups? I mean any tips on adjusting the water hose to drinking fountain.
I don't know about a drinking fountain, but I carry a device called a 'water thief'. It is a rubber cone with a hose fitting on the end, and it slips over faucets which do not have hose threads and is held in place by friction and the contraction of the rubber. I suppose that if the water fountain nozzle was round or nearly so you could use it for that purpose. It's small and cheap; worth carrying and gives you 1 more option for hooking up to water.
If I frequented a place or group of places which truly did not have any sort of faucet, but did have a common style of drinking fountain, I'd look into making myself a custom 'water thief' for that purpose. Probably some kind of bar or bracket to keep the fountain running while I filled the tank as well...
If the fountains were not common, or just could not be adapted to, then I'd consider a channel to lead the water to a bucket, and then have a pump in the bucket to feed the hose. Or if I was cheap and had a lot of time, a channel to fill a container (2 to 5 gallons), then an adapter to allow me to pour the container into the tank.