[John_AZ]

I guess you like to be the "Wild Crazy Guy" that sticks a fork in the electric socket to feel the "tingle"?

The fumes in a tank could explode by a spark. Granted a soldering iron does not create sparks but nothing is impossible.

In Old Mexico, the workers will empty a tank and then throw a burning rag at the fill tube to actually "blow out the fumes" before they work on it.

In the states chemicals are used and usually the entire tank is lifted and put in a solution of water and chemicals-after it fills the tank with the solution ---it is then welded.

But hay!
Give it a try. I am sure others have soldered the tanks and lived.

I want to make it to my 101th birthday.

John