Once or twice a week is fine for up to a month or two, but I wouldn't suggest colonics at that frequency much longer than that. Once a month is great for maintenance purposes though.
As far as tipping:NO!
That is a very old fashioned practice that from what I have been told by colleagues in this profession was prevalent 40 or 50 or more years ago, especially in Florida and Hollywood, where colonics were first popularized to a wide audience.
From what I understand, it was the influx of tourist from the North to Florida during the 1920's and 30's that established Florida as the colonics capitol of the world, a distinction that it still retains to this day. Clients, especially those from New York were used to tipping for virtually all services, and established that as an expected part of the colonic session.
I can't imagine any true professional colon hydrotherapist today expecting a tip. I have been offered one on perhaps a dozen occasions (always from an elderly client), but I would never accept one, so please don't even think of offering one.
Valerie