Was washing out some drums I picked up from the local carwash this evening (in the bath, don't tell the missus shhh) and saw that on the side of one that the primary ingredient was Potassium Hydroxide. It carries the standard skin corrosion label on the side.
I've noticed before something of an overlap between biodiesel chemical supply and carwash chemical supply, one company I used to get all my Meth from a big part of their business was carwash chemicals.
I guess it makes sense, cleaning oils off things, and the margins must be better than with us homebrewers.