Cut three strips of fiberglass fabric slightly bigger than the damaged area on the gas tank. Use standard scissors to cut the fabric.
Set the weedeater on a flat surface. Mix the epoxy with the hardening agent according to the directions on the container. Mix the solutions in a small plastic container.
Brush on a coat of the mixture to the damaged area of the gas tank and overlap it. Use a small paintbrush to apply the mixture.
Lay a piece of the fiberglass fabric over the damaged area on top the epoxy mixture and ensure that it lays completely flat and smooth. Brush on another layer of the epoxy mixture and apply another piece of fiberglass. Apply a coat of epoxy and place the third and final piece of fabric. Brush on a final coat of epoxy over the final piece of fabric and let the repair dry for 24 hours. Lightly sand any uneven areas using a 200-grit sandpaper.