Originally Posted by Minicharlie
we are very diligent with emptying out black and grey water tanks.
I previously emptied my black water every two or three days until a friend told me he didn't empty his but once a week. I always use the "bio packs" and sure enough, if I wait a full week before emptying we never get any sort of smell back up into the coach.
Plus - we never have clogs, since evidently the "bio packs" do create enzymes to liquefy the solids and paper.
I realize not all black tanks are the same size (I believe ours is 42 or 43 gallons) and generally it's just my wife and me, but you might try the bio packs plus not being quite so diligent emptying the black tanks. It's worked for me.