I keep trying to visualize what is happening. If tank is filling, then the pump seems able to draw from the fresh water tank OK so the inlet side of it is fine and pump is set correctly for normal operation vs antifreeze inlet. But the water that the pump is moving has to be going somewhere once the tank fills. OP should be having a pool of water forming somewhere once the tank is full if the water isn't coming out of a tap.
2012 Aspen Trail 2710BH | 280 watts of solar on the roof | 2x6V GC batteries | 100% LED lighting | 1500 & 300 watt PSW inverters | so far strictly boondocking