Need to know ; are the system low point drains open ?
Is the fresh tank drain open ?
What inlet ? If your putting A/F into the fresh tank fill opening and the fresh drain is open , the A/F will go through to the ground.
To circulate RV A/F through the coach systems , you usually need to disconnect , the 12 volt pump inlet and attach a pick up and run the pump to draw the A/F, from the container and pump it through the pump and through the lines, with the low point drains closed..
Have you by-passed and drained the water heater?
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.