I guess I owe an update.. here is the tank today. Gone. It sprung a leak again… but by that time, my interest waned enough that I didn’t feel it was worth resealing again. All in all, I got about 10 years out of it… about 5 years between each leak.
If I was to do anything differently and is probably good advice to any potential builder, its plan for it to leak. Most giant tanks that I’ve seen have leaks.. and more often than not, they’re insignificant. Both of my leaks were barely wetting the carpet over 24 hours. So my advice is to build it where it doesn’t matter if/when it leaks, not on the far side of a finished basement like I did.