The old adage, "If at first you don't succeed...." comes to mind. Like you, I prefer things neat and tidy....I would yank it off, learn from what I did wrong and redo it.....but...it's on the roof, you're the only one who is going to know it looks like crap.. (except the hundreds of us on RV.Net..) but I know it would still bug me....Dennis
So here's what I did. I removed and cleaned the butt-glued vent pipe extension and Cyclone venturi vent that I had imperfectly installed.
I then tried pulling up on the vent pipe hoping that it would project above the roof, but it wouldn't budge.
I then slit a 10" long piece of thin-wall plastic pipe lengthwise and glued it inside a 3" long vent pipe extension with the top of both pipes flush. I then inserted the remaining 7" of the slit thin wall inside the existing vent pipe, and installed the Cyclone venturi vent in the normal manner with lots of caulking.
I'm much happier with this installation. Thanks for all the suggestions.