Satyrn
First Post
I vote otyugh. It's a classic monster and ticks all the boxes for your scenario so far as I can tell.
I recommend naming it "Gurgle," and the churn of its stomach can be heard from a good distance away. If the PCs are of much lower level than this monster, I'd also suggest putting it in an area of the adventure location that is off the beaten path and isn't necessary for the characters to explore to complete their quest. Kind of like an optional side encounter with terrain that works against the PCs and for the otyugh, perhaps down a spiked chute and into a chamber with knee-deep putrescence that is difficult terrain to Medium-sized creatures. Injury in this place invites disease. Somewhere in the muck hides a noteworthy treasure that the cultists overlooked.
So that's what was in the trash compactor!