How to empty grey water tank

[Luke44875]

New at camping. Have 2012 kodiak at permanent campsite. The grey water tank 1 is full and the grey water 2 is empty. I only see one main drain valve for grey water under the trailer. How do I switch from tank 1 to tank 2? The drain hose drains from kitchen half the trailer but the shower side is not draining. I don't see any way to change the valve to drain the tanks independent. Any help will be appreciated. Thanks.

[sundancer 87]

There's another valve down there somewhere. It might be tucked between the axles or close to the underbelly.