>dont all soaps have the dreaded phosphates?

Nope.  Ordinary soap is usually a sodium or potassium salt of a fatty acid,
such as sodium stearate.  They are classed as anionic detergents and will
form a "metallic plate" precipitate (hard water scum) with calcium and
magnesium ions.  There are also cationic detergents, such as the quaternary
ammonium chlorides.  Both types ionize when dissolved in an aqueous
solution. Whether the ions would react with aluminum alloy, I couldn't say
[actually, I'm just too lazy to look it up.]

Randy Farchmin    --->            farchmir@milwaukee.tec.wi.us
Dept of Natural(?) Sciences
Milwaukee Area Technical College