Hi Mr. Cooties,
When you get a colonic they don't insert a long tube into you. The nozzle that they insert is actually very short, only an inch or two. On that nozzle there are two attachments, one is for water coming in and one for water and waste going out. The therapist alternates between filling your bowels with water and letting the water and waste flow out. The water is the only thing that goes in to your colon. The reason that it is considered more beneficial than an enema is that much more water is used. All of the waste is removed through the tubing and there is usually an opening so that you can see what is coming out.
I don't blame you for being nervous. I was too before I went. I actually got lost on my way to my first session and was in this really nasty neighborhood, really dirty and rundown. Anyway, I thought that that was were her office was. I was freaking out! Luckily I eventually found it and it was very clean and professional! Thank goodness.
Here is a good site to check out. It's got tons of information on colon hydrotherapy.