mostly ive been using my new camper in "dry camping" .. no water or sewer hookups .. bring my own water .. ok fine. black tank chemicals suggest i completely drain before changing to a different chem. product .. does it really matter? .. gee i have only 4 oz. of this left .. be a shame to waste it .. and a whole gallon of something different. ... its waste water! .. or is there some caustic combination that could damage the sensors and so on inside the tank? .. or a sales pitch like .. use ours and only ours or else! ..... thanks gang!