Also, empty it clear out, then fill it with water to the top before applying anything with heat. An empty tank is more dangerous to weld or solder than a full one. Your nearest radiator shop can do it, so can a local welder who may opt to braze it. Either way, that problem will never come up again that way. I agree, especially knowing how thorough you like to do things.. go the extra mile. JB weld isnt to your own standards.
