If you search for "master cleanse" or "lemonade diet" on these forums, you should get a lot of previous threads about it.
Personally, I've never tried it but after I read about it, I wouldn't have any desire to try it. It will clean out your system because of the lemon as well as any laxatives you take or laxative teas. I'm a bit concerned about the fact that you are basically drinking sugar water to sustain yourself though.
You can't out-exercise poor eating habits.