You will have to do some serious degreasing and cleaning to get any king of glue to adhere. Petroleum products tend to soak into the pores of metals, specially heated ones. Use the hottest solvent you can lay your hands on and be patient and thorough. I would go with an epoxy type like Dev-Con or JB. It's just a vent tube, just like you said, but you don't want it coming loose in there.
