I am unable to drink large volumes of liquid, so I REALLY struggled with the prep. I guess i learnt:
1) There are different preps out there, some of them taste a bit better, but require large volumes (i.e. 3 litres). I had trouble with the sheer volume of these, so ended up with a stronger prep that required much less volume of water. It was horrible tasting, but that was my preference.
2) Take your time, you generally have around 8 hours, so space it out a bit. Try anything to assist you, I tried rasberry and then lime cordial. My preference was Lime Cordial mixed with Cold water, I thought that actually was more bearable.
3) In 'my experience', you dont need to get it all down, but certainly do the best you can, I think I got about 2/3 of it down in the end.
It isnt nice, but it is doable, and it does clear you out, and the day after you will feel awsome, it actually leaves you really cleansed and feeling light and healthy. If it didnt taste so bad, Id opt to do this once a month