Oldcat - try this
link. This is the type of filter I use & it is designed to connect to a standard hose. I took the short hose that came with it, cut off the male end & use the hose to insert into the fresh fill to make filling easier. I'm certain you can find something similar at local RV supply stores.
One note of caution - I find that the first bit of water that comes out of a new filter is black from essentially flushing the carbon filter - so run some water first to clean the filter & then fill your tank.
Charlie