I actually chase both the 6pm and 8pm doses of Epsom Salt with a tall glass of water immediately after and then another glass of water an hour later. It only takes about 15 minutes for room temperature water to be absorbed from the stomach, so your stomach will be completely empty (as you want it to be) when you swallow the OO/GF. If I happen to get up to the toilet during the night, I always go back to bed via a stop at the kitchen for a glass of water.
Staying hydrated is a critical conponent of the liver flush. If you get dehydrated you WILL feel icky.
It took about a half dozen flushes for my to figure out just how much water I had to make sure that I drank during a flush. I have done close to 50 flushes over the last 7-8 years. I found having enough water in me solved the problem of getting nauseated (for me anyway), and if I stay sufficiently hydrated I always feel great after the LF.