I use Oxypowder regularly for my constipation. Iwill do multiple cleanses throughout the year to assist in this. The purpose of Oxypowder is to flush out all of the impacted fecal matter as well as any parasites that may be in there too.
I think it would be best to wait to do the oxy-cleanse until after your anoscopy. If you haven't ordered the Oxypowder yet, I would do that now. Because if your appointment is on the 12th, then ordering now would get the oxypowder to you a day or so after your appointment. I assume it would be around then. Most stuff takes 3-5 days to ship.