Decided that 5 days of electrolysis was probably enough for the gas tank. After all, I wasn’t trying to strip any really serious thick rust…just clean up the surface and brighten the metal in general. Well, it worked!
And incidentally, here’s what happens to the nice shiny coat hanger electrode:
To make sure that there were no loosely-bound rust flakes that would break off and float into the gas line, I dumped a bunch of half-inch brass weights into the tank and shook it around for a while. That was unbelievably noisy but I think it worked, because after a while water poured through the tank came out clear. There’s still some spots of rust here and there inside, but nothing a fuel filter can’t handle. Overall I pronounce this experiment a success. So successful, in fact, that I decided to use it for other parts as well. I poured a bunch of the electrolyte into a bucket, dropped in some scrap steel as an anode, and suspended the rusty kick starter and shifter linkage in there to see what happens: