I've read on a few Curezone posts that the Hulda Clark method does not allow ANYTHING after 2pm. I use Andreas Mortiz'z Liver Flush technique and do drink water if I feel thirsty, up to an hour before the juice/oil mixture. So far I have not had any problem with nausea after the oil mixture as a result of having had the water.
I do get very thirsty after the Epsom Salt drinks. My constitution has a high percentage of Vata (from ayurvedic perspective), which means I have a tendency towards dryness to begin with. I tried not drinking water after 2pm but found that I got headaches and started to get dizzy.
You may want to drink more water during the flush process.
Did the tinctures you mention taste strongly of alcohol? I use the Gold Coin Grass tincture to soften the stones in prep for a flush. The alcohol content is too strong for me, so I really need to take a lot of water when I take my Tbsp of GCG tincture. Alcohol is also dehydrating.