Where are you confused? The Master-Cleanse is a fast. There is no solid food in you. The Master-Cleanse process is going to breakdown residual matter and the salt water will rinse it out.
The SWF (Salt-Water-Flush) isn't independent of the cleanse, it's part of it. Once your clear of what you ate after the fist day there is nothing to block the path of the salt water. That's the only prerequisite.
Now, with me, never did an MC. I know what and when I eat the day before and that my next day's elimination is from my last meal from the day before. I did an SWF (Salt-Water-Flush) today. Had a morning elimination, did a mini-fast by not eating during the day, did an early evening SWF (Salt-Water-Flush) and ate light around 8pm. I'll start eating about an hour and half after the SW, whether I've expelled the saltwater or not. Just normal eating and drinking at that point, I speculate, whether it's true or not, would stimulate peristalsis, which would help move the salt water along, if it were sluggish. Tonight it took a few hours to push through, which was an hour after I had something to eat.
None of this is written anywhere, it's just what my experience and my body told me I could do.
But, again, you don't drink salt water if there is something significant in front of it. I've had insignifcant eating a few hours before that. Maybe a few grapes, a yogurt. Minimal. Light. Nothing that is going to block the water flow. It will just wash it out.
So there is an ideal way to do it, then there is the way I allow myself to do it. OK?