I'm cleaning A Parkerized Tank

[Dot Heton]

I have a gas tank that has an inch of black varnish on the bottom and a little rust, but not much. I'm thinking of using brake cleaner or similar to dissolve the varnish. I'm going to use phosphoric acid to clean the rust but since the tank has been parkerized in the past i'm wondering if the acid will remove the parkerizing. I just read 10 pages on cleaning rust from the tank and I'm leaning toward the phosphoric acid because it leaves a coating on the metal that prevents future rust. Anybody have any expirience with this?

 

[Dot Heton]

So far I've cleaned the varnish out except a couple of specs that just wont budge, even if I scrape at them with a screwdriver. I'm gonna put the phosphoric acid in at three parts water to one part acid and leave it for six hours or so.

 

[Dot Heton]

My solution drained out overnight as a pinhole opened up. At lest everything is clean inside. Parkerizing looks intact.