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.