What's the process, though? The "dissolving" is presumably rusting and then motion of water washing away the rust, but rust requires an oxygen source for the chemical reaction, and apparently Super Kamiokande has dissolved oxygen specifically removed using a vacuum degasifier to prevent interference and growth of bacteria.

I'm not feeling particularly convinced by this anecdote. It sounds a bit urban legendy. Still, I won't claim more than a high-school knowledge of Chemistry so I'm eager for someone to correct me and supply an explanation.