Can't tell if you're joking, but you have to. The doctor prescribes it, and it cleans everything out of your system. By the end, you're just crapping out the lemon drink itself and you're squeaky clean for the camera

I think he's mistaking it for magnesium citrate. It pulls water into your intestines via osmosis and makes you squirt constantly.

Your colon is like a road:

Would you rather drive down a smooth, well maintained, Clean road or a muddy mess that's never seen a cleanup crew?

You don't technically have to, but I think whoever is driving the colonoscope might refuse to work in those conditions.