It depends, shooting a lot of 4x5 in a weekend, I can exhaust a gallon of bleach in one darkroom (kitchen, really) session. Though I do cheat kodaks somewhat conservative #'s and use the older capacity guide. It's not unusual for me to process 25-30 sheets of film and 8-10 rolls of 220 in one day long session. I do replenish, and aerate, but even then, the controls strips start to show lower bleach activity after a days use, enough to spike the green and blue D-min values, thouhg I usually can regen the bleach, the last few times I've just started over as it was easier than running a half dozen control strips to get it close enough. I process by hand, though my Wing Lynch is taunting me, the fact that I would basically throw the bleach away is troublesome to me, from a cost standpoint.