Man you were brave throwing those sharp screws in there. I have used Vinegar very successfully. I have also used Molasis in a water solution, this takes longer but i think it leaves a better finish. Where the vinegar is very hash and quick, the reside has to be removed or it will keep rusting. Malasis is a ferment process so time is also dependent on temperature, (not a problem in cacti country), and fermentation reside is not as harsh and is easy to flush. In fact all i would use is a bit of 2 stoke petrol and a good rise a couple of times. No water would have to go into the tank after the anti rust process. I have done rusty tools and a rusty set of rusted gears and it works.
Gates open but another option to play with some time maybe
Gates open but another option to play with some time maybe