What does it tell you on the container?

I buy the straight stuff direct from the manufacturer who tells me the "Black streak remover" in spray bottles has been diluted 50:1 which won't do diddly on tough stains. I mix it 8:1 in a bucket for the first wash of the season and wash the trailer as normal. After that I mix it at about 20:1. One KEY POINT with this stuff is that you MUST NOT let it dry on the surface - scrub and rinse. If it dries on the surface it leaves what looks like an etch which you will never remove short of sanding and refinishing. Best to wash in the evening or on a cool day when you don't have to worry about it trying before you've done a panel! If you wear glasses and it splashes and dries on them it will leave permanent spots!