2nd floor bath. have bath on 1st floor below also. there is a wall between sink and toilet. 2 ft deep. floor to ceiling. its not a half wall. its not a stub wall. not sure what you call it. the vent pipe for 1st floor bath runs up this cavity. i want to take out wall and put vent pipe in exterior wall. 2nd floor bath is small. i hate that darn wall. is it ok to run vent pipe in exterior walls? not like it is going to freeze. its just air?