Your drain fitting is a National Pipe Thread. The thread on both male and female is tapered. Thus, the more it is threaded in, the tighter the seal. Pipe dope sealant can be a big help to makeup for imperfections. All of this requires the fitting to rotate. I doubt any kind of external patch will be long lasting.
I can't see your line from here, but many are clamped with a steel band. You can carefully cut that band with a Dremel tool. Do not cut into the line itself. Cut just deep enough to weaken the band and break it off. Use a wrench to try to rotate the fitting within the line. Might use a hair dryer to warm & soften the material.
If successful, unthread the fitting. Apply pipe dope and tighten. Get a worm drive fuel line clamp from a parts store. It can be opened to go on around the line and replace the original clamp. Good luck.