The trick to using Ospho and EP is getting it neutralized while it's WET FPOM APPLICATION.
Use it for a week or just over night, but when your done messing with rust and it's sat there dried over days....
PUT MORE ON... let it 'reactivate' the dried and crystallized residu from your last application and then while it's 'wet from application' wash it off with water.

If your metal is in pretty good shape you may just wash it off before it dries the first time...

The more thoroughly you wash it off the better your chances of it not biting you six months after your finished buffing.

I hook up the pressure washer to my hot water tank drain and use a red scotch pad or sand paper to clean it all up and basically do a wet sand paint prep at this stage. Finishing with a soapy wash down and hot rinse
The heat helps things dry faster when I hit it with the shop vac afterwards.
Like any full service Awe-(that hit my)toe salon?

Give me ambiguity
or give me something else