Hi Dylan,
I think the term "poop beast" is generally used to describe a plant/shrub/tree that is known for it's voracious appetite. The beast is typically planted near an outhouse or manure pit to help break down/absorb the nutrients in the waste, and then can be used as mulch, in hugels, etc as a way to distribute those nutrients to the edible landscape, without the risk of pathogens coming in contact with the food grown.
I don't have the link to Paul's discussion post, but you should be able to find it using the search bar. There was a lot of good information shared in that thread!
*Edit to add: Also check out the list of recommended threads at the bottom of the page. From there you can find various posts related to your question!