[fast1075]

Good repair if you don't have what is called "cold solder joint" where it does not flow. For the best low temperature solder repairs to steel, there is a solder called "StayBrite 88 (no longer in production), or StayBrite 8, the replacement for "88"". It is a soft (roll) solder that is 5% silver. You need good liquid acid flux and good technique to make it work. We use it in our line of work. It also can work on brass, bronze, and stainless.

When I weld or solder a gas tank, I drain it, dry it out, do the prep work for the repair, and use active purge with inert gas. Usually 75/25 co2/argon shield gas at a few cfh to keep the nasty oxygen at bay.

My dad used to hook a hose to the car exhaust and stick it in the tank while welding. Old School, but it worked.