Sorry let me clarify John. I always fill up the freshwater tank and use the water pump for everyday use, even when at full hookup campsites. Why I do this is a discussion for another day! 😊 In this mode, when the water pump starts sucking air, the SeeLevel shows still 13% left in the tank.
On the other hand, when I drain the freshwater tank by opening the valve like in THIS video, it drains 100%, ie SeeLevel shows “0”. This is obviously because the drain point is at the bottom of the tank.
So my thinking is the water pump suction tube is off the bottom of my water tank, ie when it starts sucking air there is still approx. 13% water sitting on the bottom, like a few others have noted as well.
Hope this makes sense! 😊