Thanks Bill, that was helpful. I think the answer is, "No one knows because the minimum amount varies from person to person and day to day so quit asking. More is better. QED."
Unless you are the one tasked with making, delivering or handling the dialysate and then it's "Just be glad you have a job." Unless you aren't being paid and then it's "Just be glad you or your loved one doesn't have to go to the center thrice per week and be treated as a carcas."
For what it's worth, considering that the only toxin that ever comes close to saturation in the dialysate is urea, and that it takes 40 to 60 minutes post dialysis for urea or creatinin to re-equilibirate, and that the rest of the toxins take up to 8 hours to re-equilibirate, I'm convinced that for most patients at home or in center you only need 10 to 12 liters of dialysate delivered over 2 hours to clear the max amount of toxins.
The dialyzer can only remove toxins that are in the blood. 10 liters per hour of dialysate delivered for 20 minutes at a blood flow of 300 mL/min will clear all of the pretreatment toxins in the blood for most patients. After that 4 liters per hour will clear all of the toxins that the cleaned blood pulls out of the extremities. (.33H x 10L/H + 1.67 x 4 = 10 liters)
I'd be happy to continue this conversation but my impression it won't go anywhere,