Solder it with the tank full of water.

Worx for me.

cliff

TIG will melt off the paint for a 1" area around the weld

I take that back, the only tank ive really soft soldered was a ts185 tank that the whole bottom corner near the petcock was completely rot. ended up soft soldering the whole damn corner and it worked very well and still holds gas to this day, but was a ton of work that i wouldnt do again. The sealer i recommended really needs no other prep work done to a tank and im willing to bet, if i hadnt leadded the shit out of that tank, i could have just used the sealer.

I was able to do the small pin holes with a soldering Iron but that wouldn't work for the larger crack. For the crack my Harbor freight heat gun got hot enough to do it, not the prettiest soldering I have done but it did seal up