Have you ever just tried plain water without chemicals? Do a search here and I think you'll find many, many experienced rv'ers only use water.
FWIW, I would never allow my black to to get completely full....as soon as my 2/3 light comes on, I dump. And we also (this is getting a little personal) flush the toilet while still setting on in as the body "sorta" acts as another seal.....and then turn on the fan after we flush.
You know, to each his own and what ever works for you is the right way to do it. It's your rv and your money.
Happy trails...
Ron