Fans should be vented to the outside! Was asked by a customer to look at a bath fan (Broan located near the shower)that was making an odd sound, sort of a whup, whup, whup. Okay, I figured something's loose somewhere. Up to the attic and discover about 20' of 4" flexible plastic duct with a goose neck in it. Upon closer inspection, I noticed that the goose neck was full of water (1.5 - 2 Gals.). The fan would build up enough pressure and be able to push past the weight of the water. Pressure drops and the struggle begins again. Drained the goose neck and re-ran the vent. I don't think installing the goose neck was intentional. It probably started out slight and grew with accumulated water.
