Black tank valve leaking?

[MaxwellD]

Greetings ,
I have a 2024 381 DB being lived in full time. On two occasions now, we are seeing water leakage apparently coming into the convenience center around the black tank valve handle (?) - can't tell for sure. The water is apparently a slow drip / slow leak and has saturated the bottom of the bulkhead and the immediate floor adjacent to ithe bulkhead in the baement. The water leakage has a faint septic odor. Emptying the black tank leaves us a little dissapointed in that the full "swoosh headwater" sound is not appreciated - in other words, it doesn't drain like a really full tank. The occupant is using a lot of water at each flush which should be a good practice. The black tank level indicators are already malfunctioning and it has shown the tank to be full almost after the first week of living in it. I am going to remove a bulkhead to look around behind the convenience center tomorrow. Does anyone have an idea of what may be going on? The grey valve adjacent to the black tank valve is left open.
Thanks,
Max