Don't know if any of you have been to the Rotax Owners site but they have some really good videos on subjects like this. In fact, they have one specifically on changing oil based on the Rotax service bulletins.
http://www.rotax-owner.com/
Over on the right-hand side click on the link for the Videos.
Another good bit of information is that purging is unnessesary unless you disconnect oil tubing on the suction side of the system. There is a Technical Article on the site that describes this much better than I can so if interested go ahead and read it.