I saw exactly the same thing about a week ago, except there was a model car with the hood open instead of a model tractor. I can't recall if it was on Neatorama or Digg, but the video looked as if it might have been captured from a kid's show like Sesame Street. So, this may not be original.

This is a scam - the water already traps the smell. To capture the residuals (the odor released before the poop is submerged, and flatulence), you need a fan to remove the air directly from the toilet-bowl area, like those fuel pumps that remove gasoline vapors from the filling area. I'm sure some Japanese washlets already have this feature.