Tank valve problems with 2014 Copper Canyon Sprinter

[Pmullally]

I searched the forum but came up empty. I recently purchased a 2014 Copper Canyon Sprinter 5th wheel and discovered the valves are seized shut on both the grey and black tank. There is movement with the levers but they will not release the tanks. I wanted to inspect the valves to see if lubricating might help but locating the valves seems more challenging than expected. I followed the cable line from a pre existing cut near the dumping connector but it appears the cable goes to the other side. Before I make any new cuts, can anyone tell me where exactly the valves are located in this model. Your help is appreciated.
Oh, I tried putting dish detergent into the tanks as suggested in another forum to loosen any dirt around the valve but no luck.

[Pmullally]

It appears the valves are open as I was able to get some flow by pushing water up through the connector. From what I can tell is that the valves are near the tanks on the far side of the trailer. My task now is to break up what ever is causing the blockage. Suggestions welcome.

[Northofu1]

Good morning and welcome from Ontario.
I would try unscrewing the coroplast from the valve side of the trailer to allow you to actually see the valves and ensure that when pulling the valve handle it is or is not moving. Other than the black tank valve you may have to loosen the valve bolts enough for a somewhat controlled drain from the grey tanks using a bucket or plastic tub. After they are empty, a full removal for inspection/ replacement.
It will be a messy job depending how much liquid is actually in the tanks.
Is there anything in the black tank?