We live in FL our dryer vent was run through concrete and comes out at ground level every time it rains water flows into the outlet of the dryer vent. Consequently my dryer smells musty all the time. I can't change the placement of the vent because it is blocked on one wall by the water heater and on the other wall by a gas line. What I was going to do was put two pvc elbows together to form an s shape which would bring the height up enough to be above grade and water and then put the dryer vent cover on the PVC however I have been told not to use PVC for any part of a dryer venting system so I have found an alternative. A rigid telescoping aluminum vent. It is usually used on the inside of a house from dryer to vent. Can I use it outside and can I spray paint maybe with high temp paint you would use on a grill to keep it from rusting?

Most through the roof stacks are galvanized or zinc coated already.

Using a flexible line for the exit from the dryer to a solid pipe,then through the roof would be the method I would do.

But.

Going through the roof just adds to a new and different problem in your area, the possibility of the flange to leak.

Would you be able to exhaust the vent through the walls at a higher height,say under the soffit?That way the problem of rain water getting in would be taken care of and you wouldn't have the opening in the roofline to leak.

Thank you for your response the dryer exhaust vent is run under the concrete floor so it does not exit the roof and we have no access to run it any other way. We really have tried to find an alternative. Our house is slab on grade construction, with a loft area that blocks going up through the roof, as I mentioned earlier going through a wall is no go due to obstacles.

The item I am suggesting using is pictured here connecting the dryer to the vent. http://www.buildersbest.com/rough-in.html I want to use it to connect on the outside of the house where my vent comes out very near the ground.

Sorry for the miscue,I thought you were wanting to use the telescoping pipework to go through the roofline.

I am surprised you haven't had rodent problems with the vent opening at ground level.

What is the exit for the vent made of?

If PVC,then PVC can be used to extend it, our furnace vent is PVC through the roofline,the heat and moisture are easily equal to a dryer exhaust.

After reading the other reviews from the posters on the site you quoted,I am leaning toward no for the use of the telescoping type vent,one reason would be that the exterior exposure can't be adequately painted to prevent rust,etc, the simple idea that the telescoping system seems that it would have bends/folds/flexibility which would expand and contract with heating and cooling,causing the paint to fail quickly.

I understand the side obstructions now,but directly behind the dryer,what are the walls made of,in and out?

SO I made the trip to Lowe's.The first thing we did was invest $37 in a dryer vent cleaner that attaches to a drill. Awesome investment. We used it to clean out the 24 ft duct and holy cow the junk it got out. What we also found was pieces of no rust coated aluminum adjustable 90 degree elbows bought two of those and two band clamps attached that to outlet and put a vent guard on it. Only thing left to do is seal the pipes together. No more dryer vert at ground level means no more water and no more musty laundry/dryer. Thanks for your help even though you didn't provide the answer you sure did help me think through and decide not to use the telescoping vent.
Thanks gunnycat

Sometimes just thinking it out does the trick:)