You need a sandblaster.........
if its to remove park. I've removed park with the proper grits of sandpaper. Flat surface like glass, bushings removed from grip, etc...
More work, patience and care needed, but not impossible
You can preblast the parts for surface roughage but the solution still etches the parts in the reaction.
A blaster makes for quick work though - a great tool to have!
"...a good thick plastic and card board will work for a tank..." No it won't. Properly done, parkerizing involves heating the solution to 190 to 210 degrees. Phosphoric acid is one of the ingredients. No plastic, and certainly no cardboard, will work.
I always used 2 pots on the stove (take your proper precautions!). One with hot water to preheat/rinse the parts, the second with the solution. Those were the final 2 of 4 containers. First was a dish soap/hot water, second was rinse.