Drains are indeed smellier when not all houses have an open soil and vent pipe, and where lots of houses use them, but the point is that if the traps are there and working and all pipework is airtight then the foul air in the pipework should not be able to escape into the building.
30ft away and you are still blaming the sink? You must have a large house! But speaking seriously, if it's that far away, I'd be more inclined to suspect a leaking joint in the waste pipework somewhere (perhaps under the floor?) rather than a trap at 30' distance. Would recommend a plumber be called to carry out a pressure test (it's not a high pressure, but it'll tell you if there is a duff joint somewhere) of your waste plumbing (which you'd have hoped would have been done already seeing as it's a newbuild).