There is a reason that stuff is sold by Bernzomatic. It is for use with a torch. You are not going to get that stuff to flow with any ordinary soldering iron. Anyone who says different has not had my experience working with it. It's for plumbing. Plumbers dont' carry around soldering irons, they carry around propane and mapp gas torches. There is a reason for that. It takes a lot of heat to melt that silver plumbing solder.

Go to radio shak or similar, get the 60/40 "lead alloy" stuff, and use it. It wont't fail you, and it will melt easily with your iron or gun. Although if you are using it for pushrods, a gun will be better IMO. Just don't get the acid core stuff, make sure it's rosin core.

The stay-brite stuff (or whatever), I can't comment on, as I've never used it. It may indeed work well with irons or guns, but why waste money when you can get stuff that will work locally--no shipping, no waiting. Go back to lowes, and get some solder called 60/40 rosin core, and go to work! One of the LHS that I frequent only sells 60/40 solder.