I use the 70ml repeatedly and then toss it, same for the stop and blix. The dev does get oxidized quite quickly when run thru the drum. I haven't noticed any visible change in the print when doing the third 8x10 worth of paper. Once I noticed the 4th one was slightly different, but that developer had been mixed for over 6 months.

The developer dissolves the dyes on the paper and turns almost purple, not a problem. I use a 30 sec pre-rinse, dev for 2 min, 1.5% acetic acid stop for 30 sec, blix for 2 1/2 min and then wash the print. I use an old Gralab timer to control the motor base, makes the timing dead simple.

If I am making an 11x14 print, the Beseler drum wants 140ml. I do the 4x5 test prints and a full print in the 8x10 and then top up the measuring cup to 140 for the 11x14 print. Same for 16x20, for that drum I use 280 ml. It's much cheaper to check for dust on an 8x10 print than a larger size.