Product review (5 stars): Limited Space for Dryer venting - MagVent is the ticket
This little gadget called MagVent MV is one of the best things I've ever used.  I only had a very small space between the wall and my dryer.  I was able to position the MagVent in such a way that the powerful magnet "caught" the dryer vent perfectly.  Once the magnet attaches to the vent, it seals perfectly without losing air.  If I ever need another dryer vent coupling with limited space available, I will buy a MagVent coupling.