Just a quick addendum... I used a "zapper" for a week to prep for a liver cleanse, but didn't follow through. It's now been around 3 weeks since my "zapping"... shoudl I do that again before I do a liver cleanse?

If you don't have obvious parasite symptoms, you can flush safely without doing a cleanse first. Be prepared to do a cleanse later though. I discovered parasite segments in stones on my 17th flush.
If you don't have serious constipation problems, you can also flush without a colon cleanse. The bowel should be open and working well to flush the liver stones on out though. Its really an individual call. You can do a liver flush, then do a ten day Bowel Cleanse before your next flush two weeks later. I've done this with great success.
Good luck and good flushing.