You could also try any brand of cyanoacrylate. Super Glue, Krazy Glue, etc. Cyanoacrylate is impervious to the damaging effects of gasoline and oil. Your plastic tank is porous, so you'll have to clean it REALLY well before you try to glue the graphics back down. Pre-mix has oil in it, yanno? I've had great results with the following procedure:
1. Drain all fuel from tank and allow it to sit for a couple of days (uncapped).
2. Clean graphics surfaces with isopropyl alcohol or lacquer thinner. (Be careful with the thinner--it will dissolve plastic if you use too much.)
3. Apply PPG brand polypropylene primer to the graphics areas and allow to dry thoroughly.
4. Apply new graphics.
The only problem with 3M 77 is that gas will eventually dissolve it. 3M 8080 is a better choice, but is still susceptible to dissolution.