On my Infinity, the galley goes into one tank and the shower/lav goes into the other. I am not completely sure but I think the washer also goes into the galley tank.
You may wish to consider a method of full tank utilization that I use: Put a final gate valve
on the end of the sewer pipe. Then leave the end gate closed and open both gray tanks. They should both fill no matter what the source of the water. Pull the end gate open to dump both tanks.
I have also used the end gate to force gray water back into the black tank assuming the grays are full. Close the gray tanks, open the end gate and dump the black tank, close the end gate and open one of the gray tanks. This forces gray water into the black tank. When the gurgling stops, close the gray and open the end gate to dump the back flushed black tank. Repeat a couple of times to use up the gray water in one tank, then close the black tank and finishing dumping both grays. That helps clean out the black tank and gives the gray water one more purpose before dumping it.