It's funny people who say, "just plain water it works for me" , well it doesn't work for everyone. RVs are all made different, some are sealed better then others, etc. etc.. IT's not like people are dreaming the smells.
I've had tank smells from time to time and it's due to the pressure inside the RV. Opening up the drivers window or the kitchen ceiling vent is usually what does it. Cracking the bathroom room window will alleviate most of the smells.
RV360's have worked well to eliminate all smells. If "plain water" or the Geo method doesn't work for you, I'd look at some vent pipe gadgets.