[Steeveedee]

The metal is hot for the solder, and when it cools, the pressure inside goes down. That would suck the molten solder into the float. I bet they kept running solder until the float cooled enough, personally. I tried that process on my leaky float, before I realized that the clip squeezed it when I put it back on (deformed it again, and it leaked, again). I put on a plastic float after that.