Full hookups with a macerator

Sounds like you have a PORTABLE macerator system. If that's the case then it's up to you to decide which one you want to use. Ours is built in so we use it all the time. I wouldn't have another rig without one. That said, grey water has a bypass, so it's open while connected to sewer/full hookups. The day I plan to empty the black tank, I close the grey valve, take our showers, then empty the black tank. I then flush the black tank with the shower water. After the third flush, I close the black valve, leave the grey valve open and complete the draining of the grey tank. When it's empty, I close everything up, finish my sandwich and go back inside the coach.....Dennis