[Steeveedee]

Yes, the large line is for the fuel pump suction side. When I dropped my saddle tanks to completely empty them (there full of old rotten gas but I siphoned most of it out first), I had to cut all the bolts. They are J-bolts, but like yours, would just turn. I bought threaded rod and installed them with a nut on each side of the mounting structure at the top so that they wouldn't spin when I put the nuts on the bottom brackets. You can siphon most of the gas out of the main tank and then pull it (if inspection shows silt on the bottom) and empty it the rest of the way. There is a way to scour and reseal the tank if it is dirty, but I have never done it. Someone will likely chime in with what they did.