Hey, that's great news, and terrific that you are booked in for a colonic.
I've had quite a few of these at 2 different operators. For me, it was important that I had full control of the water pressure so I could get the most out of the experience. Some systems do not allow for this, and the machine is located away from the bed. The system I like best was LIBBE where the controls are right by the bed and you can control this yourself once you know how:
The Therapist is also important that she/he know how to teach you how to massage yourself during the session to move more faeces. colonics are unbelievable in terms of cleaning power. I must have moved literal mountains of built up faecal matter.