[rickst29]

As Larry suggested above, and having actually done this, I still think that the original implementation is best. Let me address a few question areas from previous posts:

(1) Going into the existing vent pipe on the exterior side P-trap of the sink prevents any chance of toilet smell coming up in the sink. (The trap, full of waste water, prevents inf-flow of toilet gas.)

(2) Although the long pipe from the toilet's left side level-indicator "cut-out" is prominent, it's length and slight rise combine to assure that liquid will never be drawn into the fan.

(3) The small "computer fan" which I used is VERY quiet. I am not able to tell that it is running, except by noting the position of the power switch. (I used a lighted power switch, presenting a dim blue dot of light when the fan is on.) We turn on the fan 24x7 while camped - the energy consumption is negligible, and the room stays fresh. The aluminum tape which holds the fan in place, between the two PVC adapters from the smaller pipes to the larger fan, may be absorbing some noise in my implementation.

(4) Although the long pipe from the left toilet cut-out could be greatly shortened by swapping the position of the toilet's level indicator, (connecting the vent pipe to the right-side cut-out, very close to the sink), that could introduce some issues in long-term maintenance: The splash-stop valve might not have a lot of room to be friction fit (without glue), and the currently longer end of that pipe (into the under-sink cabinet area) might be more difficult to "pull free" from the fan fitting, for the case of a fan replacement. (per #2, the extra length may also protect from liquid being pulled into the fan.)

(5) with a short length of flex tubing between fan and the vent pipe's new "Y" adapter, both the fan side and the "Y" adapter side are easily maintained, if the flex tubing ever haves a problem.

(6) The existing DWV pipe is already mounted with a rain resistant adapter, and its location does not seem to allow for much backflow of air into an open window.

(7) With continuous airflow from a constant-running fan, the smell of outbound air at the DWV vent is nearly imperceptible (at any distance greater than around 6 inches).
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If I were doing it again, to another TM, I would do exactly the same thing.