What brand do you have? Like so many others, I am having trouble with a sensor...grey tank in my case. That sensor reads 2/3 or full even when tank is empty. I have an Itasca with non-contact, TrueLevel sensors. Tried multiple cleaners, including on traveling days. Grey water looks just soapy and does not smell too bad. Tank is semitranslucent and sides do not look soiled. So, I am now included to think it ithe problem is in non contact sensor system itself, not debris buildup. I hope cleaning your tanks works for you, but if not you are not alone. Likely I will next concentrate on learning our usage patterns to help set our dumping schedule.