Direct vent fireplace exhaust cover?

[atgcpaul]

We have a direct vent gas fireplace insert (I think). There was a draft coming in from the base so I covered the fireplace opening with a black garbage bag taped to the surround. It works ok, but air is still trying to push its way in. The exhaust goes through the wall and I thought to cover it up. However, I'm not finding a commercial solution. I could wrap a garbage bag around it with tape but my neighbor would probably appreciate a more attractive solution and I'd probably yank paint off when I remove the tape.

Anyway, I must not be searching the right keyword. Some help? The exhaust is a cylinder that measures 9" in diameter and 12" high.

Thanks
Paul

[capncarl]

Shove a deflated basketball up the chimney and inflate it.