Re: Pork & Beans Gas Tank
First clean up the area to be soldered with steel wool. It is a steel can with a thin layer of tin bonded to it by means of electroplating. Not stainless steel. Be sure the flux and the solder you;re using are compatible. If the solder has no lead in it (usually a combination of lead and tin) then it has to have a flux made for that kind of solder. If you're using silver solder it requires it's own kind of flux.
If the hole is of any size beyond tiny the solder will flow into it and down into the can. It is possible to bridge a smallish gap with solder barely molten, but if it is truly liquefied (hot!)then it will behave as any liquid and seek out the lowest level through gravitational pull. I've wasted a good bit of solder trying the impossible. Another can is perhaps cheaper than the propane and solder. Also take care that you're not using too much heat. When soldering the bung or petcock heat the thicker metal directly and not the can itself. The can heats up a lot quicker than copper or brass fittings. It also helps to tin the fittings first (apply a thin coating of solder to the fitting before soldering it to the can). It makes the solder bond better. When you're done wash the soldered areas with water and baking soda solution as that will neutralize the acid in the flux... else it will eat into the can and cause it to rust much faster than it would otherwise.
Keep at it and it will get easier.
Someday when I grow up I will probably lose interest in toys with wheels, but until then...