I took a look at the site and can't see anywhere that says what kind of colonics they administer....although it mentions self-(something-or-another) which suggests to me that they are probably open system...not what I would recommend. Give them a jingle and find out what type of system they use...open or closed....and let me know....I will tell you more then.
As for prep before a colonic....the best thing you can do is to be relaxed and very well hydrated. The experience will be more pleasant and you will release much more.