Do you really need to remove the tank? Empty, it's weight is neglegible. All you'd have to do is empty and clean it out real well. And, while I've not done the mod myself, from what I've seen on YouTube, the Composting Toilet is just installed (with some modifications) at the location of the original toilet.
Mike and Cindy
2016 Tiffin Allegro Open Road 34PA
2018 Chevy Malibu