Product review (4 stars): Lint Trap Kit
I used this to vent the dryer out to the garage but made a few alteration to the unit for it to work correctly.  Under the cover I used a wire mesh the size of the the unit then put a piece of window screening on top of that and the a piece of filter on top of that.  This way it keep all the lint in the unit and does not go all over the place.  I clean it once a month and that seem to be enough.

The unit does not trap lint on it own.