Wel. with RA-4 in drums the challenge is actually wetting the print with the amount of fresh chems needed. I replenish RA-RT blix at 20mL per 8x10. So with drums it would be say 100mL to start, and re use that for four prints, then start to add 20mL per print after that just to be sure.

Pour off the surplus and accrue it for HHW disposal, before adding fresh stuff. I used to work with colour coded plastic mugs with open bottom handles that would hang over the edge of the wash basin that I used as my tempering bath. The mug had a line drawn in with a sharpie at the 100mL level.