They will interfere with the breakdown cycle. Your tanks are holding tanks and nothing more. Waste starts to break down etc, but really you dump before most of that happens. Now where it goes after that is the issue. Despite every detergent company under the sun saying you have to have all these harsh chemicals,they actually kill the bacteria that breakdown waste and stress septic systems. So, will it harm your system in your RV? No. But they aren't good for the septic systems you dump into. Vinegar and lemon are excellent for cleaning most anything and aren't as harmful to the necessary bacteria.