I have a 4 tier wedding cake coming up and it requires filling.
I am terrified of the whole thing sliding apart.
Just how tall do can you make the dam? I want to put plenty of filing in it but I'm just not comfortable with it.
Any tips or tricks?
I would suggest torting the cake so you have 3 layers of filling for each tier, which should be plenty of filling. I usually make my dam with either tip 12 or just with the plastic coupler. I've never measured it but my guess would be probably about 1/2" tops.
I think this link might answer some of your questions: