....which could lead to another round of exploding-toilet stories!

But seriously, this is one of those situations where the solution to pollution really is dilution. Wastes are "hazardous" to the extent that they accumulate in the environment to toxic levels because they don't get bio-degraded, e.g., heavy metals, organic solvents, cancer chemotherapy drugs. But things like strong acids and strong alkalis are harmless once they are diluted enough not to be directly caustic to living tissue (or to sewage treatment systems.) Our stomachs secrete 0.1N hydrochloric acid which equates to a pH of 1.

A few years ago a railway tank car derailed somewhere out West and, on rupturing, released its load of 80-odd tonnes of sodium hydroxide into the adjacent river. A bunch of fish died in the first mile or so downstream but beyond that the river was just a bit more protected (temporarily) from the effects of acid rain.

I would be curious, though, about what, exactly, leaches into the de-anodizing solution from the parts being treated. Aluminum oxide, presumably? No more harmful than an old storm door sent to the dump?