Outback second grey tank?

[Cbw4x4]

Looking at purchasing a 2016 keystone outback 3216rl. I noticed a second waste port near the rear with a valve on it. There is the main waste port in the center with 2 valves. All the literature I can find does not show a second grey tank for this model. Does anyone have this trailer that can enlighten me?

[St8-e]

I have a ‘16 298RE with the same dump outlets...the valve with the 2 handles is the Black tank and Grey Tank 1 (Shower/Bathroom Grey water). The one valve by itself is Grey 2 (Kitchen Sink Grey tank)

[Jayc71]

I have an Outback 260UML, same grey tank setup. You can either swap the hose around when dumping or pick up Y adapter to connect both tanks to a single sewer connection.