It is essential that both inflow and outflow tubing be sterilized between client sessions. Most colon hydrotherapists who use these type gravity systems with autoclaved ss speculums change the tubing after each treatment and put them in a bucket of sterilizing solution for at least 24 hours before rinsing and using again.
During a colonic, reflux can occur during both inflow and release (reflux means the flow is reversed, waste from the colon can back up through the thinner inflow tubing), and it is also possible for backflow to occur through the fatter waste tube, particularly when the therapists pinches it off to help stimulate release.
For these reasons you should insist that your therapist use only freshly sterilized and rinsed tubing during your sessions. I suspect she may be doing that already. This is just standard procedure.