Well, the back label says (in red): Concentrated Acetic Acid (35 %) which is corrosive and damaging to surfaces. Then some more warnings about breathing fumes, keeping it away from eyes and skin and children. Rinsing with large amounts of water and contacting a physician. So I plan to treat it as if it is 35 % Acetic Acid. But what strength should I bathe my valves in?