I have a heating/ac unit in my second story attic. The condensate line is plumbed directly into one of the vent stacks. I am getting some 'sewer gas' odor on that level when the heat kicks on and guessing that the fan is pulling through the condensate line from the vent pipe since there is no water in the line. How are these lines normally handled on a multi level house? Should I install a trap in the line or should it not even be put into the vent line? Thanks!