For decades, I have simply used odour treatment in my holding tanks. Years ago, I stopped buying the expensive toilet paper and just used cheaper household stuff. I have never had a problem. I have the dock hands rinse the tank with water with every pump out. Recently, someone at our marina replaced a leaky tank and over a few beers, we decided to cut the 27 year-old tank open and see exactly how much "stuff" remains. Surprisingly, only a couple of inches of what used to be toilet paper was stuck to the bottom. In the cottage, during the 70s and 80s we used to drop yeast in the toilet on Sunday nights to help the composting in the septic tank. Worked very well. Does anyone out there do anything or use anything that they have found to be helpful in breaking down fibres in their holding tank? Crappy topic, I know.