i used to use dk50 quite a bit, and if 777 is anything like that ---
you replenish it after each run, but then when you process "X" amount of film through it, you dump 2/3 of it and mix the olde with the new. the olde stuff "mellows" the new batch, so you don't have to wait as long for your film to look "perfect" . the cloudy/mirky "toxic waste dump" effect is what you are looking for! so your film isn't too contrasty, but "just right" ....
at least that was the way dk50 worked ...