I do add about a cup of water and mix it all up in a bowl. We put her in our jacuzzi and fill it up as much as we can and then put the mix on her back which is where her skin is so dry. You need to leave it on at least 10 - 15 minutes (if pup allows). The I rinse with plain water (no shampoo at all). I put the vinegar in a spray bottle and spray it on the places with the most flakey skin.
It works seems to work well so far. Poor pups and their itchy skin!
I also started adding a capsule of fish oil to her food today. Maybe that will help with the dry skin a little. I'll let you know if that helps!