Cannot exactly visualize your setup but if they both come out the same drain versus separate then yes run the macerator. It will be much quicker.
Some macerators have a gray water bypass. That is, you can leave the gray tank valve open and the gray water will slowly drain. This is handy when you have hookups and use the shower a lot etc. But before dumping the black tank it is best to hold back the gray so you can clean the lines with it.
Certified Senior Electronic Technician, Telecommunications Engineer, Telecommunications repair Service Center Owner, Original owner HR 2008