I did a builder warranty inspection in Nampa Idaho, the home owner complained that every three to four weeks she would have to drain about a gallon of water out of her dryer vent line. She has been having to do this for the last 7 months. She had the builder out twice to look at it and he said there was no problem and didn't know why it was happening. His solution was it was her dryer. I should add that the laundry room was on the second floor and vented out the roof.

I didn't take to long to figure it out. Who ever installed the vent cover didn't know how to read. "remove screen for dryer" The screen was plugged so no moist air could not be vented and was running back down the line to the dryer, but unfortunately leaking out in the attic causing mold and water damage.