Most of the rusty stuff gets soaked in Evaporust, then the small stuff like I recently did tumbled in a rock tumbler with sandblast grit for a day or two. I have also sandblasted larger stuff before plating.
You do need to get the rust off, or the zinc won't stick. Electrolysis will work, but I haven't tried that. My son-in-law has a setup for that using a plastic trash can and a battery charger.
