fresh tank drain plug has bad threads

[excellaf350]

anyone ever have and issues like this? My trailer has always had the tiny leak from under the trailer. I thought it was probably the drain valve hose or something. there it a 12x12 area of the belly pan under the fresh tank that has rusted quite a bit so today I decided to open her up fix it. I pulled the inspection cover and cut out the rusted part of the panel. To my suprise the drain valve and hose were not the source of the leak but the main tank drain plug was cracked. I pulled the plug and looks like it has actually deformed itself in there and since its been there for so many years it actually deformed the threads in the tank. When it came out it cross threaded on its way out. I dont think its ever been out before looks like factory sealan on it and no one in theri right mind would have put that plug back in.

I went to the hardware store and got a new 1.5" PVC plug. The nipple in the tank is still very plyable and is easily flexed with my fingers not hard like the cap. Now since the threads are sort of damaged I figured I would try to seal it up with some pipe dope... nope didnt work. Tried it again with about 6 wraps of teflon tape on her and again no luck. Better but not a complete leak stoppage. It develops a small drip of water every few min. I decided I am not dropping the tank out of this old girl so I cleaned up the threads and dryed it out. Then put the plug back in with RTV I'll try to fill it with water tomorrow hopefully it stops the leak. Not sure what else to do if it still leaks at this point. Anyone ever have damaged threads int eh main fresh tank drain plug? What did you do to fix it?