Hi just invested in the porta potti 165 for the caravan and just read the manual. Now the manual says put detergent in the bottom part and add bout 4oz of water but a few people have told me there is no need to add water to the bottom part and to just pour a bit of the detergent into it, Also the manual states to just add fresh water to the top tank and states DO NOT ADD DETERGENTS TO THIS TANK but everyone has said i need to. All i wanna know is wot is the proper way to fill these things up please or which way does everyone else do it, thanks