I'm sure the flush out is a real neat feature, but alas, I too don't have it.
What seems to work well for me is that I just dump the tank and add chemicals if it's a long trip and then dump at the end with some of the remaining fresh water that I purge before the trip home.
For me, once home, I flush the tank out really well. I have a poke through sewer line next to the driveway. At home I don't have to worry about bacteria or someone else's mess draping though my trailer since is all clean and I know where the gear has all been.
I have also noticed that some dump sites don't have a garden hose connector making the flush feature I have seen not work without mods.
Anyway, just thought I'd share what I do in case you come across the same type of dump station.
Computers manufactured by companies such as IBM, Compaq and millions of others are by far the most popular with about 70 million machines in use worldwide. Macintosh fans note that cockroaches are far more numerous than humans and that numbers alone do not denote a higher life form. -NY Times 11/91