I never, ever fill the potable tank from sources any where near the dump station which generally is not an issue as usually the spigots in the campground are threaded. Where things get a bit frustrating is at many State campgrounds and all camping areas in the National Parks we have been to, those non threaded faucets that have to be held open drive me nuts. Set off to find a 3/4" Fernco to make something and bought this from Lowes until I can get all I need to cob my own version together.
www.danco.com
What I quickly discovered is that to assure a perfect fit on all faucets you will have to remove the black internal rubber piece (pulls right out) AND get the next larger size clamp-this allows for a very snug clamp that will not blow off due to the small diameter/very high restriction of the product-mine will be much better but until I get it together this works just fine for me-and I hope for you also should you give it a go.

55/64 in.-27M or 3/4 in. GHTM Clamp-On Garden Hose Aerator Adapter - Plumbing Parts by Danco
The Danco adapter connects a female garden hose to an unthreaded faucet and vise versa. It is made of low lead brass and is chrome-plated for greater durability to endure the rigors of everyday use.
What I quickly discovered is that to assure a perfect fit on all faucets you will have to remove the black internal rubber piece (pulls right out) AND get the next larger size clamp-this allows for a very snug clamp that will not blow off due to the small diameter/very high restriction of the product-mine will be much better but until I get it together this works just fine for me-and I hope for you also should you give it a go.