Acid wash or Picklex

I have read lots of discussion on the use of acid wash. I would like some details of the application and precautions. I have a product called Milkstone Remover and Acid Rinse. (about $15.00/gal) The label is Phosphoric Acid (75% solution) 56.33%
Other Ingrediants
Surfactant, Dye, Water 43.67%

Do I dilute this futher with water or use as is?
How long do I put it on the metal?
Do I rinse with water and let dry?
Do I need soda in the rinse?
The painters will use PPG epoxy primer. Any precautions there?
We are doing this on rusted sheet metal that will be sandblasted first.

Or, would I be better off getting some Picklex 20?
I would appreciate any thoughts.
Thanks

As I have said many times before, Picklex 20, if whatever you are painting is down to bare metal. It is used as a protectant, or for minor rust conversion. If you are going to sand and paint right away, you don't need anything, as long as you have mechanically gotten rid of the rust in the pits. I live in a dry climate and have no need for anything. However we have had about 3.5 inches of rain in the last month, humidity has been unusally high. I have two 38 inch rims I sand blasted about 2 months ago sitting against my overhead door, where humid air and any moisture can get inside. There is no rust at all on those rims or on any of the other parts I blasted sitting on shelves. I get flash rust instantly if outside, but none inside. You need to be careful and take care of your bare metal, but it is not an emergency unless you have to let it sit for a long period of time. In a 24 hour a day humid climate what I do may not work. If you use Picklex 20, there is no need for anything stronger, and you do not need to wash it off. Prior to painting just scuff off any white residue followed by wax and grease remover, it works every time. BUT, if you cannot get rust mechanically out of the pits, you still use Picklex 20 and then use the scuffing and wax and grease remover. No need at all for acid wash, Picklex replaces that and works just as good. Picklex is expensive, but does not need to applied heavily and a little goes a long way.

It is my understanding that all rust converters are basically the same. I use a product that apparently no one else has heard of. The product converts the rust to an oxide. I do nothing to neutralize it. No rust, no chemical activity. I just prime and paint. Never had a problem.

As I have said many times before, when I was picking up paint for my dump truck body that I was sand blasting, the paint guy at the jobber told me that I needed to acid wash before priming, so I bought a gallon for not a lot of money and used it. At about the same time a professional body shop owner friend took side panels from one of my tractors and prepped and painted them for me as a favor. There were a few pits where a foam insulation strip had rubbed on the metal for years. He had cleaned the panels to bare metal but after three years there were bubbles where the pits had been. None of us want this on our tractors. The same has happened on another tractor in a place where the paint is rubbed every time that the tractor is put in gear. Both were painted by intelligent people who know how to paint but that work mostly on newer cars and not the old rusty stuff that we work on. Just because it appears to be rust free doesn't make it rust free. It depends on how long you want it to last. I got a bottle of the expensive stuff at my local auto parts store probably two years ago and followed the instructions and I could see where here and there it turned black indicating converted rust in places that I thought I had the cast or steel clean. I see that as a very good thing. I also read on the container that it is phosphoric acid, which I knew to be the same as in milk stone remover but for much less money. I use it all the time. I spray it on full strength or dip small parts in a container for ten minutes. I then wash off with plain water. If I don't wash enough I get some white residue, but this comes right off with another application of the acid and a little better rinsing. I may get a little flash rust but the epoxy primer handles that much more easily than rust left to grow in pits. If the air is humid I will wipe it dry after rinsing. Your rusted sheet metal is a situation where the acid is of great benefit, as I am sure that with all the work you are doing that you don't want rust bubbling up out of pits under your paint.