Oh wow, a topic for which I'm somewhat of an expert.
Get a box of cornbread mix. Dump it in a bowl. Add milk. Stir and then consume with a spoon. If you want some violence to your shits then mix a considerable amount of crushed red pepper before the milk while it's still a dry powder. The milk will help dull the impact of the CRP as you're eating it but not as it's passing, and passing fast.
With this method you should be able to make a load of poop that floats a bit and will pile up above the water line, significantly increasing the stench you leave in the bathroom.
The amateur enhancement is to also slam down a number of Fibercon tablets, but if you want to amp this up to pro-level defecation then go look in the supplements section for some stuff called "chitosan". It's like ground up shrimp and crustacean shell, and it bonds to fats so instead of being absorbed they pass through you. That plus a bunch of fatty stuff from other suggestions you'll be receiving will take your adventure to the next level. This plus swapping in heavy whipping cream for the cornbread concoction then you'll probably have bowel movements so horrible you'll have to register them with some kind of government agency.
Good luck and may your toilet paper be the good stuff.
Basically, your body can only produce so much Lactase (the thing that breaks down Lactose) at a time. Lactose intolerant people barely produce any Lactase, which is why eating a tiny bit of cheese is OK for them, but they'll explosively shit themselves if they have a glass of milk.
Anyways, you have a lactase limit, time to find it. An added bonus of this strategy is that your options are a bit more varied: You can load up on cheeses, milkshakes, cream puffs, cheesecake. Regular old milk has the most lactose though, so if you want to shit yourself plentifully and violently, bring a ton of that (and whatever other foods you want, the milk will do the work here). Just don't try and chug a whole gallon of milk in under 20 minutes, you'll vomit because it will dilute your stomach acid until instead of digesting it, it'll curdle in your stomach.
So uhh, step one: get cholera (it lives on shellfish, and plankton do with this what you will, lick some shells or something)
Step two: ingest cholera
Step three: try not to die
Not said yet but just some salt dissolved in water. I remember not pooping for a week coming out of a hospital stay that had me on morphine. Tried the stool softeners and such. But lemme tell you. An 8oz glass of warm water with a teaspoon of salt and 30 minutes later it was go time. When I say go time I mean be ready, when it hits there will be no delaying it.
You need nuts/seeds. Peanuts, sunflower seeds, almonds, walnuts, pistachios. Any high fiber nut and seed will do. If you can get it in bulk, the better. Like 10lbs should last you for well beyond 10 days. But if you need to shit your brains out, well, uh. There it is.
Again this post? I mean of course you are doing the opposite version, the original one asked what to take in order Not to Poop over those 3 days but damn. Is this a new meme or shitposting trend?
If you have any preparation time, then Psyllium husk (sold as metamucil for one brand example) with lots of water. This would win on sheer volume, HOWEVER, if you take too much then constipation.
Half a spoonful a day with at least 2 cups of water
Come over. I'm sure I can cook you some diarrhea-inducing food. It'll be spicy as hell, so sweating and peeing gets sorted too. And I'm sure it's not going to be easy to find.
Not what I was expecting in my feed, not going to lie. But I think as strange as this question is, it bodes well for original content on Lemmy... unfortunately.
That being said anything with a laxative effect should do the trick. For lots of pooping and sweating you could go with the sugar-free gummy bears on Amazon.
So,... to pass your D-test... :D... Laxative in recommended doses, liver and kidney purifier as Uroperine (again, recommended doses), and gallons of water ;-)