I didn't have to drink anything for my defecography. They just shot enough barium up me to see if I could expel it. It didn't take long at all! That was a breeze compared to my small bowel study. On my small bowel study, I did drink 2 big cups of barium!!! Horrible, and horrible trying to get a week's worth of stool and barium out of me that weekend. For me, no prep, just nothing by mouth after midnight. Also, they told me no laxatives for a couple days. I think laxatives could speed up your system, so I think you should lay low from them for a couple days. Better check with the doctor though! Good luck!