1964 Bambi Sewer Question

This is really going to be a newbie question.



Our 1964 Bambi has one lever near the bumper. I am assuming this is the release for the sewer. My question is which water is the lever releasing:



1). Black water

2). Black and Gray water



and if the answer is 1). Black water then my assumption would be that the gray water runs out of the outlet all the time.



thanks in advance.



Huan