Today I managed to start the process of sealing the gas tank. After dumping out a half cup of rust particles (only one pile is shown but there was another), I added the cleaning solution. Probably not really needed in this case as there was no gum inside to removed but I did it anyway and am letting it soak for the prescribed time. The little dark spots are pinholes so I’ve got to be sure there is sealer on the inside top surfaces when the time comes. The steel is quite heavy-appearing other than those spots.