On our Coachmen Pursuit Motorhome the Bathroom sink drains into the black tank. This was because of the black tank being right under the bathroom floor area and the gray tank being more to the other side of the frame. The kitchen and shower drain into the gray tank.
Just have to watch when people use the bathroom sink not to stand there running water. People and friends that camp under stand this. Others think they are at home with the water at full blast and 5 minutes to wash the hands.
2014 Coachmen Pursuit 31BDP
2016 Ford C-Max Energi
1987 Chrysler LeBaron Convertible
FMCA Member #F438633 - Good Sam Life Member
Coachmens Owners Group Member