I suspect that it may be the vent/overflow tube for your tank.
Underneath your coach somewhere in the vicinity of your axles you may see another blue PEX tube with a shutoff valve attached to the end. This would be the fresh water tank drain valve.
If it is closed, open it.
There is a chance that the check valve at the water pump is allowing your tank to fill with water and it is now overflowing .
Peace
Dave