Holes in sump

[John Mason]

I soldered a tank some years ago. If soldering fuel tanks take all the necessary precautions I.e. no naked lights and thoroughly wash out the tank beforehand. I also filled the tank with hot water to just below the area I wanted to solder in an effort to remove any petrol fumes. I used hot water so that the water did not act as a heat sink and maybe the heat evaporated any residual fumes from the air pocket above the water. Do not use to hotter water otherwise you have a problem with steam and thus not dry for soldering.
I have also heard or having exhaust gasses passing through the tank whilst soldering to stop residual petrol fumes exploding.

John Mason.