I actually do all my pushrods with a bog-standard propane torch from the hardware store.

I also use rosen core flux paste and rosen core solder. In a perfect world, this is the "wrong" solder to use, but I've had pushrods bent in to pretezles in mid-airs, brass couplers broken in half, servos, cleveses, and control horns broken, but never a solder joint failure. So the solder joint is obviously stronger than anything else in my control linkages.

Basically, put a little paste on the metal rod, put it in the coupler, and gently apply heat. The paste will melt and fizzle. Then pull the torch off, and touch the solder to the metal. The solder should flow in and make a nice smooth, shiny joint, a nice smooth fillet. If it balls up, one of the parts wasn't hot enough. Try applying more heat.

If you see black gunk appear, you're burning the flux, and have the torch too close, too much heat.

It does take some practice. But once you get good at it, it goes quickly. When I'm mass-building combat planes, I can make a dozen identical rods faster than it takes me to type this message. (well, ok, maybe not that fast. But still, very quick)