On my 2004 350Z, the Fumoto valve installed easily and didn't need much tightening to be leak-free.
However, on my 1988 Supra, it wouldn't stop weeping even after tightening it as much as I dared. So, I bought a new drain pan, drained out the $50 worth of Redline oil, and removed the valve. Then, I cut a second gasket out of some material I have lying around. After reinstalling the valve and oil, it doesn't leak, though it still took a fair amount of torque to make it that way. The plug is 18mm, which is pretty large, so can take a fair amount of torque.
Basically, if your car's oil pan is smooth and flat around the drain hole, the gasket will seal well. If it's not so flat and smooth, you may get to add another thicker gasket in. The gasket the valve comes with isn't very thick.
Asterix