Here is a anodizing site someone recommended to me:
http://www.kingoftrim.com/home.html
As for the purple stuff, most of them are about the same. I have used several different brands with the same result. I have about 10 gallons of it that I use and then pour back except for the last little bit of dirty junk at the bottom.
The purple stuff does absolutely nothing for rust but it is great for stripping paint from plastic parts without harming the plastic, and now as I have just found out, it is good for stripping anodizing from aluminum via a chemical reaction. Oh, and it will strip your outer layers of skin from your hands if you dont wear gloves.
Dont bother using liquid drain cleaner. From your link, it only is about 1% to 5% Sodium Hydroxide versus the powdered form which ranges from 30% to 60% Sodium Hydroxide. Oh, by the way, it is so comforting to know that Crest Tooth Whitening Strips have the same active ingredient: Sodium Hydroxide. ;-)