I would NOT expect the neighbor to replace it, let alone at full cost . . . . .  He's the neighbor, after all..
Stuff happens and as others have asked, how old is the tank ?
Has it sat outside when you had it or did you keep it inside ?
You could have easily set up your neighbor for failure and now you want to take advantage of him/her -
THAT's NOT RIGHT ~
Of course, you need to give us more info to properly JUDGE you  * * *  *

( * * * donates sarcasm)