I'd take a look at the hose running from that gravity fill port to the tank, and also the vent hose, to make sure they aren't kinked.
My vent was. It was just too long and jammed in so it was kinked. If I remember correctly, it was venting, just not well....
What I'll often do before a trip is to drain the tank completely. Open the drain and let it go while I go about loading or whatever.... when it stops, I'll fill the tank. mostly I do this when the unit has been stored for a while, just to get fresh water in there...but it could be done easily just to "recalibrate" things for you.
My guess is that it's nearly empty, but the vent is kinked and so it's not filling properly.... just a guess really.
has it filled ok in the past?
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