Mon Nov 25 (above)

YES... the bathroom "overhead fan" draws up fumes through the RV toilet when flushing.

The above photo is my attempt to keep oders out of the bathroom when flushing by adding a "vent fan" on the black water vent. I previously had a similar "vent fan" on there with a power source from the inside which ran for more than 2 years before the fan started making sounds of going bad. Being powered from inside I started worrying that at some point it might overheat and create an ignition source...on top of the gas in the black water tank...in the middle of the night.  Knowing I had to replace it I redid the whole thing without the 110v > 12v power source. This time I powered it from the bathroom "overhead fan" which is powered only when we turn it on when using the bathroom.  

Problem: The "overhead fan" takes about 30 seconds for the lid to open (and close) via a small motor and the fan itself is not "on" until the lid opens most all of the way. Thus while ideally one would choose to close (turn off) the "overhead fan" prior to flushing so as to not draw in the fumes, no one wants to wait 30 seconds for the "overhead fan" to shut down before flushing. Therefore by having the added "vent fan" running on the vent to the black water (at the same time the "overhead fan" is running) it maintains a negative pressure on the tank. Thus the "overhead fan" no longer pulls in fumes when flushing after making a boom boom.  And .... during the day (sunny out) the solar keeps the vent fan running for those non boom boom (non overhead fan use) flushes. At night the vent fan does not run and that is just as well with me as it always made me nervous running all night in case something should go wrong.

PS: Not seen is the final addition of a vent cover to keep it dry during the rain.