I was reviewing this thread with an eye to setting up an electrolysis rig and figured Arm&Hammer Washing Soda is the most likely and readily available product hereabouts.
Here's a link that lists all a whole lotta N.American household products that use sodium carbonate:
http://householdproducts.nlm.nih.gov...tbl=chem&id=16
I don't see that CLR stuff they're always trumpeting on TV - I got some to clean the rust stains in the toilet - expensive. Haven't tried it yet.
Note that the Arm&Hammer is >= 86% concentration, but that Prestone cooling system cleaner is 90-98% (along with some other potent ingredients)
I also have some of that commericial grade caustic soda stuff for cleaning coffee pots - it does brilliant job on my coffee thermos - but nasty to use, fine powder goes aerosol when disturbed, not nice to breathe. It would probably be great for rust removal, too.