Jerry,

That is a turtle-vent cover... look at the bottom of the "turtle" shell-type cover and look at the top of the vent pipe. Now, how are the massive amounts (pun intended) of sewage gasses going to be sucked into the attic??

Oh, I'm sure it could be with the fan motor reversed and a WILMA force wind blowing into the attic vent. But then, if WILMA were to come back then there would also be tiny tornadic activity in the attic where funnel clouds of insulation would surely be swirling also.

Now, without the fan motor being reversed and there not being much of a possibility of WILMA coming back, or atleast in Warren's neck of the woods, I just don't see that drawing gasses into the attic.

Richard