Mcneilms, What you may be seeing, after metalprepping is not necessarily rust. The acid (phosphoric acid) converts rust, or iron oxide, into iron phoshate. The difference is that iron phosphate is inactive, and just lays there. You can paint over it and it won't deteriorate. Some times it appears gray, or has an irridescent look.

I don't know what is available to you there, but I use an R-M product (801 metal prep) that contains alcohol, and you don't rinse it. You just towel it dry. It leaves a lot less of the iron phosphate behind.