I think that you must be refering to the amount of solution used when developing with a rotary processor. I use rotary processing for 35 and 120 film, in a Unicolor film drum. In order to keep things simple, I only use one developer, D-76, diluted 1:1. For one roll of 35mm, I use 4 oz of solution (2 oz dev, 2 oz water) for one roll of 120, I use 6 oz of solution (3 oz dev, 3 oz water). You only need enough solution to cover the film as it rotates.(posted 9307 days ago)To find the volume of your tank, You can adjust the tank for the number of rolls to be developed, fill with water, then measure the amount of water. Then use a little less than half of that amount. The rotary tank only needs to be less than half full, at the most. I have found that when developing more than one roll at a time, the developing time needs to be decreased, in order to avoid excessive contrast.
I usually develop Delta 400, for contrasty subjects, 13 minutes, low contrast subjects, 17-18 minutes, both at 68 degrees. Times could be shorter at higher temps. Of course, if you are using a conventional tank, and adgitating a few seconds each minute, the tank must be filled to the top in order to keep the film immersed at all times. Hope this helps, it works pretty well for me.