[Maritime Q-Scout]

I think I solved the problem.

I went to Hone Depot to get a draft blocker and foil back insulation. Brought it home.

Cut a larger hole in the ceiling to have better access to the vent.

Then realized the hole in the boxsil was like it was an open hole outside. The draft between the the pipe and the side of the hole was immense.

I returned the draft blocker and foil back insulation, and picked up a $10 can of spray foam insulation. Filled the sucker.

Draft stopped.

It's currently colder than your ex's soulless heart outside and yet the laundry room is fine.

Thanks for the help everyone. It appears the issue was far simpler than we thought.