As promised, attached is a "cook book" set of instructions for replacing the ST1300 lower fuel tank.
The removal and installation took me two days.... three if you count associated jobs such as upper tank removal/installation and bleeding the brakes from having unnecessarily disconnected a brake line. It took this long because I stopped at every opportunity to take pictures. I also took plenty of breaks to relax and think ahead.
I thought about posting the instructions as a regular post but there are just too many pictures to mess with.
The likelihood that you'll ever have to do this job is pretty remote. I was just "lucky". Background on why I had to replace the lower tank can be seen here: