Magnesium sulfate / potassium sulfate / sodium sulfate
"Let me preface this by saying I had gastric sleeve 16 months ago. My stomach holds 6 ounces. Took me 20 minutes to get the first prep drink in. I've forced 16 more ounces of water in and I'm in some serious pain.  It's been 54 minutes and I'm trying not to throw up. I gotta get another 16 ounces down in 20 minutes. Then do this all over again at 5:30 tomorrow? Oh I had to do a pre pre prep last nite. 10 ounces of magnesium citrate. That was worse tasting than this stuff."