We have a second home nthat was completed in 2003. We have a septic tank system. Occasionally we can smell septic gas odors in the second floor bath that is adjacent to the master bath. I have noticed that when the master tub is drained we can hear a girgiling sound eminating from the adjoining bath room. At times we can notice the smell in other parts of the home, so it is somewhat difficult to detect where it comes from. I do know for certain that the main smell problem is coming from the second floor bath that abuts the master bath. How can we rectify the problem.

Since you are hearing "gurgling" it leads one to believe you have a plugged or obstructed vent line and the system is attempting to vent through the other sink. Also check to see if you have an Air Admittance Valve (AAV) under the sink. On occasion they will fail to close and sewer gas will vent through them.