I have been checking most information on line. I did see a fuel system diagram which shows that this may well be the fuselage fuel tank drain valve (cap). That's my guess now. So, if someone finds  something different, please let me know. Thanks to everyone out there who looked.

Need help identifying the indented area just forward of the hydraulic vent and located below the wing root on fuselage underside. I can see it on some P40E kits but not on others. Any information would be appreciated.