[Flatbedford]

I spent some time on the tank last night. First I poured a couple tablespoons of Simple Green and water into the tank. I put the cap on, plugged the threaded nipple with my finger and shook it for a while. With the garden hose I filled the tank until it overflowed and then let it drain a couple times. When it was full of water I plugged the bottom hole with my finger and watched for leakage. There were a few leaks right where the threaded tube is attached to the flange that is soldered to the tank.
I drained the water and blew air through the tank with the exhaust from my shop vac. After that I piped some exhaust from my '70 F350 (the dirtiest exhaust in the driveway for sure) into the tank. After all that I figured I could work on the tank without much fear of explosion.
With a wire wheel on my Dremel tool I cleaned the area thoroughly. I smeared flux around all the suspect joints and went at it with MAPP torch. I was surprised how much heat I needed to work the silver solder, but I was able to lay a nice bead around the suspect area.
After some cooling time, I chipped the flux off and did some clean up with the Dremel tool again. I filled the tank with some water, plugged the hole with my finger and watched. No leak. After shaking as much water out as I could, I threaded the valve/glass bowl assembly back onto the tank and closed the valve. I put about a cup of gas in the tank and checked for leakage. Still holding. I dumped the water gas mix and refilled the tank with some more gas.
I left it out side over night and there is still no leakage. I guess I have fixed the tank. I still have to get some paint on the tank where the torch burned it off and I will be replacing the valve/glass bowl assembly before I put it back on the tractor.
Looks like I have fixed my leak with minimal expense and without any explosive gas fume mishaps. Thanks to all for your input.