Bill,
Assuming that your coach is equipped with a power water hose reel you won’t have a standard city water connection with a built-in check valve. Open the access door inside the wet bay, look to the right of the hose reel and you should see the freshwater check valve. I’ve attached an image showing the location on our PT.
Another thing to consider, if your coach has the full version Aladdin (shows the status of the freshwater tank) the autofill function uses the tank fill level to know when to shut off. Are your tank level readings accurate? If not, you will need to recalibrate your tank levels. When using the autofill, you should see an ‘AF’ indicator on the freshwater status line, does the freshwater tank continue to fill after the ‘AF’ indicator turns off? If so, then your problem is likely as Eric explained.
-Scott