Locate and turn off the water shut-off valve that supplies water to the tank.
Find the shut-off valve that controls the flow of gas into the tank and shut it off.
Attach a garden hose to the drain valve on the gas tank and run the hose into a drain or stationary tub. Open the valve and drain the water from the tank.
Scrape the area around the damaged area with a putty knife to remove any loose pieces of metal.
Mix the epoxy and the hardening agent that came with the fiberglass repair kit according the instructions on the kit. Use a medium-size plastic container to mix the ingredients.
Cut the fiberglass fabric into sections that are big enough to cover the damaged area and overlap it by an inch. Cut three or four sections.
Place the first section of fabric over the damaged area and brush on the epoxy mixture. Ensure that you completely cover the entire surface of the fabric.
Position the second piece of fabric over the first, with the grain of the fabric running the opposite way from the the grain of the fabric of the first piece. Brush the epoxy mixture onto the second piece. Again be sure to cover the entire surface of the fabric. Repeat this process with one to two more pieces of fabric. Let the patch dry overnight. Turn on the gas, relight the pilot and turn on the water supply to the tank.