I have had good luck with KO to get rid of holding tank odors in the past. This year it is just not doing the trick. My bottles are old (I bought a few last year and left them on the boat over the winter). I wonder if they have gone bad-all the good germs have died. I called Raritan and did not get much help. The vent seems to not be clogged as the odor comes out when we pump the head. Any thoughts?