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If memory serves, the PBY was known as the flying gas can and had a tendancy to go up in massive explosions if/when all that fuel ignighted or do I misremember?
The PBM was noted for fuel leaks, wither from the tanks or the lines I don't know.
The PBY, according to the manual (available in the tech section of this website) had two large "fuel spaces" which could be used sort of as is for fuel (unprotected) or a series of protected fuel cells could be installed in the space/s cutting the fuel capacity by hundreds of gallons. Manual gives the option of fitting only one space with protected fuel cells and using the other space "as is".
Hmm, in my somewhat limited experiences with the fairer sex that was reversed!