You probably have two gray tanks. 1 is called gray, 1 is called galley, they have no cross connect. Your galley sounds full. Of course you also have a Black tank.
The two hose bibs are your hot and cold water low point drains for winterization.
2011 Keystone Sprinter 323 BHS. Port Charlotte Fl/Hinsdale MA. Retired Master Electrician. All Motor homes are RV's. All RV's are not Motor homes.