The water filter is probably not the problem, but in case it is, mine is located under my sink. It comes with its own plastic "wrench".
However, this issue is probably at the city water fill input. The screen needs to be pulled out, and flipped around so the cone is facing in...which opens the valve to begin the vacuum process.
2015 Jayco Greyhawk 31FS-"Scamper"
2015 Subaru Forester 2.5i Prem. 6 Spd
Blue Ox Aventa LX Tow Bar
2014 Jayco Jay Feather X23B-"Glampy"(Sold)
DW, DS, DDx2, and Bandit & Fletcher