[jcranmer]

> IIRC, PP can be a precursor to chlorine.

Converting KMnO₄ to Cl¯ would require a nuclear reaction. Chlorides are generally soluble, so it's not going to cause an insoluble salt to slowly dissolve as a permanganate salt precipitates instead. It does appear to be a stronger oxidizing agent than Cl₂ (and Cl¯ and ClO¯ and ClO₂¯), but there are likely better reducing agents in most water than dissolved chlorine ions.

[zzazzdsa]

For what it's worth, permanganate is an extremely strong oxidizer (probably the second strongest stable solid oxidant known, after persulfate), but at neutral pH it is unable to oxidize chloride to hypochlorite and beyond. (The electrode potentials are too close, and anyways the maganese dioxide byproduct turns hypochlorite to chloride and oxygen.) Instead of reacting with a reducing agent in water, (the main possibilities are simple organics and ferrous iron, and these turn to carbon dioxide or insoluble ferric oxide [sidenote: this is why permanganate is added to water in the first place]) permanganate tends to break down to oxygen and manganese dioxide, which settles out.

[stagbeetle]

My wording was vague, you'll have to excuse me.

[mulmen]

I wish I knew enough about chemistry to know if you are providing valuable commentary or pulling our collective leg. I will give you the benefit of the doubt.