I replaced the upstairs kitchen sink. Had to use new p-traps, etc, since the new sink was deeper than the old one. This is a two basin sink, one side has a disposal. Since this replacement, which -did not- involve me doing anything to the vent pipe, I'm getting sewer gas coming thru the downstairs traps on my bar sink and washing machine. This only happens when I use the upstairs sink. If I put the stopper in the bar sink, and fill the sink with water, I can actually see the gas pushing past the stopper, and bubbling up thru the bar sink. Help! (and thanks in advance).