W/D Hookup - which gray tank?

Hi There,
I have a heartland Edge toy hauler with hookups in the back. It has two gray and two black tanks (two bathrooms). I am guessing the second gray water tank includes the back w/d hook up. How do I know for sure? I don't really want to rip the underbelly off to see... is this a common sense conclusion?
Shellye

I don’t know your model but a couple of ideas:

I can trace my lines from the basement. Taking down the wall is a good thing to do anyway.

secondly get some food dye and dump it down the washer drain pipe. Flush in a lot of water with a hose and then see which handle gives you the color.

great idea! thank you!!!

Just put some stinky Pine Sol in the tank or drop some color dye and trace it out pulling the valve open.