Toxin build-up in the body is a continuous process. While the rate of toxin build-up is related to how we live, it would be virtually impossible to eliminate it completely.
When a person requires dialysis toxins are only being removed during the session if at stage 5. Between sessions the body is unable to remove toxins as they build up, potentially causing damage over the longer term.
Best Practice for Hemodialysis states that more is better. That is more volume by time not speed.
How much is enough? In reality only a kidney can provide enough toxin removal but the guide for dialysis patients is short daily or extended (8hrs+) every 2 days.
The following Replaced Kidney Function calculator uses session time to provide a rating of how much dialysis you are getting when compared to a kidney. Try it out and see how you are doing.