City water backflow into fresh water tank

Thanks for the part numbers. I've been planning on doing the same thing. For now I just close the valve between the tank and the pump. I suspect there is construction debris in the pump's built-in check valve. My TT is less than a year old, and I have always used an outside filter.

I was glad I had a full tank the other day when our campground lost water for 7 hours after an underground line broke.