So I know we all make the bathroom stink on occasions but our master bath tends to get a sewer smell in it at times.  If I had to guess I'd say it happens more often when it's windy.  The vent for the shower and tub is a 2" PVC pipe.  Is it possible that when it is windy it gets the water in the traps moving up and down creating a suction and causing an odor from the septic tank?  Would putting an elbow on the vent tube stop this?