Recycling Rusty Fasteners

If I'm not mistaken, according to the company literature, it does not require a neutralizer. I don't rinse with water and have never had a problem in ten years. However, it could not hurt anything to do so.
I'll repeat the company info here is case it was missed in post #5:

"After the Ospho reacts with the steel surface it is completely neutralized and does not leave behind any film or deposits that might interfere with subsequent primer/topcoats."