I do know that at the QB factory they have what looks like a spa bath where the finished tank is actually submerged in for testing. So theoretically it should come to the customer leak free.
Having just finished a build where I tested the tanks in various ways however found the bullet proof way was to fill it full of fuel, leave and see what happens. The reason fuel is the way to go is that the blue staining makes it easy to see a leak or weeping rivet.
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