Sounds plausible. When I was being told how to use my Sani Con system, the dealer said I should empty the black tank then turn off the Sani Con and open the grey water to let it flush back into the black tank, then close the grey and continue to dump the black. You would be doing pretty much the same thing.
Brian, Loretta & Daisy (Golden Retriever)
2008 Holiday Rambler Endeavor PDQ40
2014 Ford Explorer toad