Neat idea !!! Having a separate holding tank (pipe) frees up volume in your grey tank, and it does not look out of place and being black, blends in champion!!!
One more step to having a complete kitchen on the outside of the RV. It’s your RV accessorize the way you want it. Just like a chicken truck some say they don’t need to do a large car like that but if that’s what you want so be it.
If you add another power port, you are essentially creating what electricians call a suicide cord situation. The prongs on the 30A RV plug would energize when you plug in. I would get a 120V coil relay, and wire it so that when you connect power it disconnects the RV outlet.
