We are also in a park with their own waste water treatment system. Chemical are not allowed. Most of these type of parks will be out in the country and NOT on a city water system. We personally just use lots of water and no chemicals. I hate the smell of the chemicals and we do not have odor problems if everything is in working condition as it should be. We also never leave a mess at a dump station. Maybe you are smelling the accumulated stuff in the dump station holding tank while the lid is open ??? That stuff sitting in there smells much worse than what is being dumped.