On Sat, May 15, 2010 at 7:59 PM, Alistair Bell <albell@shaw.ca> wrote:
> plastic pipes are fairly resistant to the concentration of lye used
> in proper drain clearing application.

My father had a company that sold 99,99% NaOH. It was packaged in
ordinary plastic bottles. I have filled probably thousands of those. I
still have several kilograms of that stuff.

NaOH, KOH, H2SO4 and HCl are way too strong bases/acids for any metal
surface in my opinion. Theres a difference in rates acids work with
corroded metal and healthy metal. All these named in previous sentence
are dissolving also healthy metal quite fast. With phosphoric acid and
iron for example, the rusted iron molecule is reacting with acid way
faster than healthy iron. Thus You are doing less damage to the metal
while removing certain amount of rust.