I would not advise a "colon cleanse" for anybody. They can be dangerous and even if they don't cause a gastric event they can leach important stuff out of your system. Besides they are unnecessary. If you have no gastric symptoms your colon is nicely balanced, thank you very much, so just leave it alone!
I've had 2 colonoscopies. I can tell you that Vodka and Tonic Water are clear liquids! Even if you skip the vodka, tonic is a good mixer for the stuff you have to drink! Or at least it made me think it tasted better