I get the fuel cell concept: fuel (H2) and oxygen combine to make water, which is thrown overboard. But, I don't see how this pertains to flow batteries. Gene

I get the fuel cell concept: fuel (H2) and oxygen combine to make water, which is thrown overboard. But, I don't see how this pertains to flow batteries. Generally, the flow battery material (e.g. vanadium oxide) is highly toxic and/or reactive. Do you propose sending that type of material overboard?