Why the heck would you bother feeding the Tarrasque? For that matter, why bother keeping it concious? The whole point is that it's an indestructable beast that keeps going, no matter what you do. If it was up to me, I'd have crews working 24/7, carving the thing down to the bones and then hacking away at the skeleton. Of course, it's going to keep regrowing, but you should be cutting off as much as possible.

I wouldn't see a point at throwing slaves into it's open mouth, besides being cruel or part of some wierd cult.

That said, and entire city build around slicing open a regenerating monster and using it's body parts? The first thing that comes to mind is that they probably wouldn't limit themselves to just the big guy. Small-time organizations who aren't licensed to work on the Tarrasque anymore will probably keep troll or werewolf in their basement, for "cheap rations" or similar products. Heck, the slavers may be buying the slaves to turn them into werewolves, for the renewable-meat and -spell components market. Perhaps they were already "infected" by the werewolf slave handler, and they're just waiting for the next moon back in Bael Tarrasqa for the change to complete.