Separate pipes for black and gray tanks

PawPaw_n_Gram wrote:
The black tank is almost always located directly under the toilet. RVs don't have the water flow from the toilet for a run any distance to the tank.

Another clue is often the size of the pipe running to the dump outlet. A black tank pipe will be 3 inches in diameter. A gray tank is normaly 1 1/2 or 2 inches in size.

If it were my rig - I would get some food coloring and make sure I had a clear 45 degree elbow to attach at the outlet.

I'd go to a dump location, empty the tanks. Then put water colored with one color into the toilet. Open the dump valves in turn and see which allows that colored water to drain. Repeat with the shower and a different color, and with the kitchen sink with a third color.

That way you will be totally positive which handle/ valve drains which tank. You can change labels if needed.

You might also want to try it with a fourth color and the bathroom sink - just to know if that drains into the black tank or the gray tank. Some rigs do it either way. On my current rig, when I look under the sink, I see the drain going off at a 45 degree angle to under the shower, not directly down into the black tank, so I know the water goes into the gray tank.