[ZenGum]

I think I had one of those when I was in Japan. IIRC:
Fasting, thick chalky drink, roll over three times, photos, laxatives, and funny things happening in your bowels afterwards.

Don't gulp the drink down too quickly - one of my cow orkers said this can cause a bubble which will look like a problem leading to an unnecessary follow-up gastroscopy (camera tube down mouth).

Expect a bleachy white turd (or several) which sits in the bottom of the bowl and won't flush.

No major drama. Just be mindful of where the nearest toilet is, and if you don't get moving soonish, take another laxative. You'll be right.