I, and others, were only pointing out to the OP (and others, including you) that black tank chemicals (much like special rv toilet paper) is not necessary, nor required, and is only making your wallet lighter. 
 Ron 
But that's just your opinion and what you believe.its certainly not absolute fact like a few here try and spin
Chemicals in may cases are required, are necessary and do work very well
To each their own way of doing things
You like water then by all means use it.I think all natural chemicals are the way to go so I use them by choice
90% of the time my tank systems is perfect but like said take a 2/3 full tank and warm weather and stinky fumes will and do come out the roof vent.If u have the fan on input you can and will at one time or another get a wiff of unpleasant odours if not treated properly with a proper chemical.
as said to each their own. water works for some just not for me
forgot to mention another reason I use what I use is it breaks down the solids fast and therefore no worry of solids plugging up things