Originally Posted by DR Buck
Agree. But, depending on your model and size things may be different. My 36 ft V3200 is as described.
My 39’ 2018 Voltage 3305 is the same as well. And on the walk through it was never pointed out. I found out on my own the first time I went to dump and removed the sewer cap and water started pouring out despite the fact my valves were close. Eventually, I found the 2nd grey valve in the back as described.
I also noticed on my trailer there is a sticker on the bottom of my trailer indicating the valve location which I never noticed the first time.
@OP, take a look and if your trailer has the galley sink and washer/dryer hook ups in the garage I bet you have the exact same valve location in yours. I would speculate if your model has a rear bathroom that the grey for that bathroom goes there too. I am sure the manufacturer saved money by not using a cable valve and connecting it to the wet station where the others are located.
On my rig this rear tank is “grey 2” on the monitoring display.