I copied his. It is very easy. I got ABS pipe at home depot for like 5 dollars for 10' and a 90 degree bend for 2. The valve was 40 from amazon. The glue was roughly 3 dollars. It all went together and I tested it after it dried, no leaks.
I literally just cut off the grey water valve and put the 90 on it and did a straight shot to the valve, it lined right up. It looks really nice that way and the grey can be used to flush out the black water from the hose after each dumping, which can be daily in these popups.
Thank you for sharing your info 2gwright, I may not have figured that out on my own.