Don't be too discouraged about not seeing any stones at first. I didn't see any stones my first flush either. Most people on this forum will say that it's not uncommon to not get any stones with the first few flushes. Each flush is different. Just keep in mind that whatever you are flushing-- out is better out than in!
I drink water on the day of the flush up until about 30 minutes to an hour before the ES. Being hydrated is important. I also keep a cup of ginger tea beside the bed for nausea and take sips of that when I wake up through the night.