Garage tank question

[hillegom]

That would work on FW
However, all hot water tanks have a sacrificial anode, made out of zinc, inside of them. A long rod, that is changeable by the way. Just like aluminum fish boats and lower legs on boats, they all have a sacrificial anode. So I don't think that this zinc would be any good for the inhabitants of the SW tank.
FYI If you want your hot water tank to last longer, then change out that anode every 5 years. Not everyone will tell you that. My last tank went 20 yrs and longer, I sold the house before the tank went.