Moped Army and Remlr.com are some of the places where you can find tutorials on gasoline tank repair. These websites provide step-by-step instructions to troubleshoot and repair various problems with gasoline tanks.
Moped Army offers a detailed instructional article on each problem highlighted. The site offers categories of repair information, and all you need to do is click on gasoline tank repair link to get the associated tutorial.
Remlr.com provides a how-to tutorial to illustrate how to repair an S3 fuel tank complete with images to show the various stages of repair. The tutorial outlines the requirements and what to do to repair the tank.