I reuse it until I've run enough rolls through it that it starts going pink. Though I can't imagine the alcohol in it at the 1:200 dilution not preventing mold growth. Though aren't you're only going to get mold if you have contamination to begin with.....
I put a drop (or two for sheet film) of 1:3 "stock" solution in the final distilled water rinse and pour it down the drain.
This is the last stuff your film sees before drying, why do so many risk fungus and other contamination???