Greg, they make elbows that are adjustable from 90 degrees to about any angle less than 90. If you can go through the floor and make a 90 degree bend to a foundation vent under the deck, that sounds great. Might consider using hard duct though as the lint does not tend to collect near as bad as in flex duct.
Hurry up and get this dryer vent finished so you can get the heap ready for Harlan.
