[robocat]

That is active.

Something passive could be submerging the tank in a pool of water (also good for proving spill containment won't leak).

[cyberax]

Typically you don't have enough surface area for that. The walls are thick enough that thermal conductivity into an ambient-temperature liquid alone is not going to be sufficient.

[colechristensen]

Uh, you can't just disconnect a pressurized 35,000 gallon tank and drop it into a an enormous pool you just keep full under it at all times.

[bagels]

I think the passive version is the tank stays in a pool all the time.

[robocat]

Riiight. That is exactly what I was thinking.

[colechristensen]

It's really unclear what you were thinking