It is my understanding that Epsom Salts really dehydrates you. Therefore, I drink water up til about an hour before the 6 pm Epsom Salts . An hour AFTER (at 7 pm) I have a glass of water. And an hour after the 8 pm Epsom Salts I take another glass of water (9 pm). This has had no effect on my flushes at all - they have all be successful (7 so far).
At 10 pm I take the oo/gj mixture and do not have any water until the following morning because oil and water don't mix and it can cause nausea.