Tips for removing rust from a gas tank include parking the vehicle in a place that is free of clutter and flammable items, draining all fuel from the tank, disconnecting all fuel lines, and using muriatic acid. Remove the fuel tank from the vehicle before cleaning it.
To remove rust from a gas tank, first unfasten the drain cork to empty the tank. Detach all fuel lines, including the supply line, fill tube and vent line. Unsecure the metal straps that hold the fuel tank in position, use a wrench to unfasten the nuts holding the tank in place, and pry the tank out of the vehicle. Place hot foamy water in the tank, wait for a few minutes, and clean the tank with a pressure washer to remove any lumps of rust.
Measure equal parts water and muriatic acid. Pour the water into the tank, and then add the acid, taking care not to drop any acid on the exterior of the tank. As the acid is highly flammable, have a fire extinguisher nearby. Allow the acidic solution to sit for 30 minutes, and drain the tank.
Put 1/4 cup baking soda in a small container, fill the container with 2 gallons water, and mix the contents. Pour the solution into the tank, let the solution sit for a few minutes, and drain it out. Repeat the process as necessary. Pour isopropyl alcohol into the tank, wait for 10 minutes, and empty it. Fill the tank with gasoline, let the fuel rest for 10 minutes, and drain the tank. Secure the tank back in place.