the original tank cavity was between the stringers with two bulkheads fore & aft to enclose the tank. there was a 1" hole in the bottom of the bulkheads and a piece of 1" pvc was glassed in the bottom and the holes were sealed to keep the cavity "spill proof". the theory was if the fuel cell ruptured, the fuel was still contained in the cavity and not get to the bilge. pretty sure it never worked like that though. then 4 wedges were put in the cavity to hold the tank off the bottom and off the pvc pipe. after that, they were foamed in to stabilize.
when i installed my new tank, i eliminated the thru pipe and enlarged the drains
