Where is the leak
Is the leak in the tank or at one of the piping outlets? If you are just repairing the tank then the advice below is all fine. If the leak is at one of the pipe connections then you are going to want to get it brazed. Solder will hold for a while but as it works from pumping and turning the stove on and off it WILL crack and then you end up with a big leak. Let me say, this kind of thing can really wake you up when you have a cigerette in your hand. Play it safe and get her brazed!