If you check valve is stuck open or defective, when you tie to a hose you will gradually fill the fresh water tank as the pressure from the hose will push back through the pump the same way it would if it were bleeding back. Have had that happened on rigs, but really rare.
Someone suggested early on in this thread to try air pressure and I often resorted to that when I was checking out a rig and couldn't find the leak. Sometimes you can hear what you can't see.
I was just looking at the Northern Lite owner's manual and see that it shows Flair-It fittings rather than clinch bands. That means a load of connections that are hard to tighten.
