Welcome to the forum!
My recommendation is to go with whatever the physician tells you to take. Each of them has their "gold standard" (for some, it's Fleet phosphosoda; for others it's Golytely; for others it's the pills; some use the pills plus whatever liquid nastiness they prefer the most). But the reason they use these techniques is that they are tried-and-true, and you don't want to go in for a scope unless you are thoroughly cleaned out - otherwise, they won't get a clear picture of your colon. And who would want to go through that again?
I haven't done a lot of research on colon hydrotherapy, but I doubt it's as effective as any of the aforementioned techniques, so I wouldn't take your chances just before your scope. If you did go that route, you certainly should ask your doctor about it first. If s/he finds out you didn't follow the prep instructions given to you, s/he might have a cow.
Just my two cents.