Another side question: What's to stop the PCs (or the large creature) from dumping the cauldron over? Would you allow the large creature to pick up the PC and drop them into one of the cauldron without a save (assuming a successful grab attack and moving a grabbed opponent)?
Edited to add:
I don't like being able to Bull Rush a hanging opponent just because that square is adjacent. By that logic, if I have a power that push a target I should be able to throw them up into the air as many squares as I can push them and that is obviously not the intent (and maybe expressly against the rules).