Yes, if you have the anode out and anything runs in there (AF or water) it should be flowing out the hole (if the trailer is level.) So the question remains--where did the 4 gallons of AF go? If it didn't come out of any of the faucets, shower head(s,) ice maker (if you have one,) or toilet, you have a leak somewhere (possibly open low point drains?) or a cracked pipe from the ice.
Are you sure the pump actually sucked out the jugs of AF? (I know, stupid question.) Just because you hear the pump running doesn't mean its actually sucking, especially if its blocked with ice...
2015 XLR Hyperlite 30HFS5 (mods being performed regularly)
2009 Salem LA 292fkds (gone)
Nights- ('12)23 ('13)23 ('14)15 ('15)31 ('16)25
2014 Harley Davidson FLHX (XLR cargo)
2014 VW Jetta TDI (diesel sipper, camping support vehicle)
2011 Ram 2500 CC 4X4 CTD, B&W Companion (toy hauler hauler)