Hapooning a fuel tank is the process of reomving fuel tank and reducing the lenght of the filler and the vent tube protruding inside the tank to aid in refilling. Benefits include less auto shut offs from pump when trying to top off, also adds small additional capacity. Last fillup i was able to pump in 38.5gals.
If you looked at my pics, unfortunately I did not get any during the process but I they showed what I removed from both the filler and vent tube.
I used a set of pvc pive cutters, removed the sending unit reached up inside and cut as close to the opening as possible.