The "variables" is what persuaded me to fill mine with water before wedling on mine.

Was it more trouble than just welding it w/fuel in it? Sure it was ....

It took a while to drain fuel, fill with water, then get the water out

BUT

I'm still here, with all 10 fingers and 10 toes.  I know ~plenty~ of you guys have welded on "live" stuff, but I just a little too paranoid.. to each his own, I suppose...