This is odd

[Yakman619]

You can just wrap some aluminum foil over the top of the carboy. Once active fermentation stops then you can put the airlock on if you like.

Thanks. I let the lock dry, sealed it as best I could, then wrapped the base with saran wrap. It's a ghetto rig, but it should hold up.

[Ozwald]

You can just wrap some aluminum foil over the top of the carboy. Once active fermentation stops then you can put the airlock on if you like.

+100

The StarSan is your culprit. As long as there's positive pressure coming off from it foil is a great (& arguably better) substitute. In fact I can't remember the last batch where I actually used an airlock at all. A coffee filter is not a good idea.