If the inboard plug is leaking, it will come out the same place mine did… from the center of the fuselage. It will leak into the center spar, where there is a hole to drain from. If it’s leaking that much, I suspect you’d see evidence under the plane.
If you’re not seeing any fuel leaks, I’d suspect you might have the same problem I did… the short length of fuel tubing between the sump drain and the fuel tank sump fitting may have split and is weeping.
In the attached file, the first is the left tank, and you can see how clean and dry it is underneath the hose. The second picture is of the right tank, and you can clearly see how fuel has been weeping and discoloring the aluminum for quite some time.