well, i flushed the tanks, filled partially with water, put in the orange baggies of whatever that stuff is and some lemon scented grey water treatment.. drove it 20 miles and drained it. odor remained for days, put several ounces of lemon stuff in the grey water, two orange baggies and four full toilest of water in the black tank and the smell is gone a week later. Now, i know crap stinks, and because its gone the scent stuff killed the residual odor, but the problem was what was stated here that i found in a great thread. the vent cap under the sink was only on by one turn. i removed it inspected it and re-installed it. i feel confidant this was where the odor was coming from and suspect it is fixed.