Dump valve question

I apologize if this is a re-post. I searched and could not find one just like it.

We're just over a year into owning our 2011 North Country 27BHS and the wife asked me this weekend how I knew that I was, in fact, dumping the black tank first, as they are not really clearly labeled. I told her I was REASONABLY sure, as I paid attention at the walk-tru. She went on to ask if I was absolutely, positively 100% sure...

To which I responded, "Well, NOW I'm not!-)"

There's 4 labels on the body of the tailer above the valve handles. One above the left handle says "Waste Water Holding Tank", but the label right under it says "Sewage Water Outlet". Then on the right, one label makes advisory about using the hose attachment only when valve is open, and the one right under it says something about "most states have laws about dumping sewage, yadda-yadda"

Can anyone tell me which of the two valves I have is Grey and which is Black?

Thanks so much for any help!!

I don't have your model but if you got a clear elbow for the drain there would be no question. Try looking at camping world or some other RV supply.

Ditto on Mike's suggestion. The only way to really know for sure is to get one of the clear 30-45 degree elbows.

Get the clear elbow....your eyes and nose will tell you which is the poo-poo tank. Most of us use those so you know when its clean. The one marked "use with valve open" is the black tank flush. Personally when I flush the tank I do close the valve to let it fill up and then dump again. Everytime I do this I ALWAYS get more stuff out. It usually takes 3 flushing to get clear water out. BUT NEVER WALK AWAY WHILE DOING THIS....NEVER....EVER. Cause if you do the "POOP" demons will get you. Get a cold one and a chair and sit right there. BTW, always make sure that you have the water pressure reducer on the flush hose and never...ever...use that hose for your fresh water. Your 1'st drink of fresh water after that might be your last.