It's because I've been needing to fix for at least 10 minutes that I am throwing it away. To be honest with you when I started doing my own B&W back in March again I didn't think I had a chance; six+ gallons is too much fixer to get rid of. I have one left, and that's going to my old "darkroom" place this weekend; they recycle the silver (or something, I don't know what they do with spent fixer, but they don't throw it away).
If I fix with normal times, the negatives do indeed have a purplish tone (specially if it's TMax; that sucker takes twice as long when fresh), so I just agitate normally during five minutes, and then for the last 5-10, I let it sit, with one round agitation in the last minute. And then rinse well, and let it sit in washing aid for twice as long.
Being cheap is expensive 😉 In my defense, I could not find Ilford rapid fixer here at a decent price, and I buy 5-10 litres at a time. B&H does not ship film chemicals (nobody that I'm aware of, actually). These just came in today because of the new school year. So I bought 5 (I don't want to mix too many so I don't have old fixer in the future).
By the way, always, always change your Photo-Flo mix, every 3 months the most, no matter how infrequent you use it (one month if you use it a lot). You don't want to fight any deposits when you're squeegeeing (sp?) the film.