I'm not sure that I could explain myself monosyllabically enough for you to understand.
The petcock on these tanks only flow gas when there is engine vacuum. Some bikes have an off switch on the petcock, but the GZ doesn't IIRC. So, just pull the down tubes from the petcock to the carb, making sure you notice where they go. It's not hard to figure out. They are sized to a length to really only fit on the right way. Some gas will sprinkle out. Catch it if you want but there is really no need to.
Then, under the seat, there is a bolt (maybe two; it's been a while) Then you juts lift up slightly and push the tank towards the front of the bike and pull it away.
TADA!
BTW, Plus one to adding an inline fuse, no matter how you wire it.