black water valve

Bad hose? Black tank valve leaking? coming from leaking tank? residual left over from dumping?

There's varying degrees of "empty", depending on how level you were the last time you dumped. That would explain having some liquid in the tank(s). If the black and grey gates are completely closed, there shouldn't be any drips even if there is liquid in the tank(s). If you have a screw on cover outboard of the gate and its tightly closed, then nothing should be leaking, even if the gate is slightly open. If that's the case, put a bucket under it until you can get it serviced.

The seal /gasket in the valve could have gone bad, but more likely a piece of toilet paper is preventing the valve from closing completely.

Open and close the valve again. There should be no leaks with the ale closed properly.

fill the tank and dump it again, X2 on something keeping it from closing all the way, you might be able to "flush" it out of the way