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If you have a 3 valve , water heater by-pass , with the valves in the correct position , there should be no water entering the tank.
Any water entering the tank could be an indication that the cold in or hot out valve is leaking.
There are plastic plugs available , at RV parts stores, to block the line fittings that screw onto the tank , you'll need two and they are about a dollar each.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.