Sprite and magnesium citrate. A dose takes about 30 minutes to work, so if you dilute it in a 20 ounce bottle it should hit at about the 2 hour mark depending on how your body reacts.
I lost 7.5 lbs in one night due to that stuff. I went to the doctor because I kept having diarrhea. Turns out I was so constipated the only thing that could make its way out was liquid. I drank a bottle of that stuff and 45 minutes later...well...you know that one scene from Dumb and Dumber? Yeah, that was me for like an hour and half straight.
Hopefully the shortage isn't still going on. There was a huge shortage a couple years ago and I couldn't get it anywhere. Had to resort to an enema to prep for my surgery.