We use a SC Johnson product called Scrubbing Bubbles. It is the model with a wand and disposable pad. The advantage is, we are eliminating a bottle of liquid. Rather than concern about the black tank, I would be more concerned with the plastic toilet bowl.
Paul and Janet Braun
2003 Toyota 4Runner V8 now 2012 Toyota Sequoia V8
Escape 19' 2010 now 2014 Escape 21'