Disease causing microorganisms such as bacteria from your black tank can wiggle their way right back to the filter, does it protect you from water born pathogens? Probably not, hence the reason RV manufacturers don't connect the two systems. Get a different colored decicated water supply hose for the black tank and dry it completely between uses, or have a good supply of antibiotics on hand.
2017 F350 Dually 6.7 Diesel
2014 Silhouette 299 RKDS
Nights Camped 2016 - 43
He who dies with the most tools, wins!