tonic stuck

[Ashtoreth]

Spoiler below!

The well right in front of the prison cells' door shouldn't be covered with red crap. I just loaded a save from my game, and even after I prepared Weyer's Tonic, the well is still open.
There's no need to throw a rock inside the well while the Kaernk is eating the meat, just wait a bit and pull it back after he finishes the meal.
Also, you don't need a pot specifically for the poison gland. You'll mix the poison with the blood inside the glass jar that's in your inventory. Have you collected the blood already?