Often, if your body is low on magnesium, some of the ES will be taken up by the body.
Spirit the originator and Webmaster wrote a long time ago, that you don't have to have diarrhea during the evening.
See his post //www.curezone.org/forums/m.asp?f=447&i=8513
I personnally like to be empty and have buttpee when I start the flush, so 3 evenings before I use Oxypowder or ES, but that is just because I prefer it. It has nothing to do with the protocol.