I have a 3 year old home and get sewer gas odor from one of the two sinks in the master bath when the sink is not used for several hours. After 10-15 seconds the smell is gone. I think I have isolated the odor coming from the overflow. This has been going on for a year or so. I'm going to sell the house and think this may be a deterrent.

Sounds like you've picked up some nasty bacteria in the overflow in your lavatory.
The solution would be to fill the tub to overflowing with a 50% of water and bleach. Let it overflow so bleach gets into the cavity in the overflow section. Drain and flush out. Let me know if this helps , Good luck, Tom