It certainly sounds as if there is a leak some place in the suction line from the tank to the pump. My pump has a strainer, not a filter, on the suction line close to the pump. You could check the strainer, if you have one, for suction leaks; mine had a leak where the clear bowl screwed on to the base.
Do you have a winterizing connection? Its a short length of hose that can be put into a gallon of antifreeze to allow pumping antifreeze through your fresh water system. There is a valve on that hose and a valve on the suction hose that goes into your water tank. Is the valve to the winterizing hose closed and the valve to the suction line to the tank open? If those valves were not in the proper positions, your pump would suck air.
Check these things and let us know what happens.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch