OK, new experience this last weekend. We met the brother-in-law & his wife at a large commercial RV "resort" (his choice, had a bar on the premises). Hook up the slinky, connect hose to the screw-in elbow going into the ground connection, hose falls out. What? Closer exam reveals that I have somehow managed to lose the gasket that resides inside the elbow and makes the connection tight. Trip to Wally World the following morning, $4, and I am back in business, with a spare gasket to boot.
Moral: carry a back up gasket.