Second and third on the tap and the silicone.
Its after the horse got out but you never ever thread a plug into a coupler that you welding maybe a thread or two but thats it. The coupler expand and what I call jump the thread ( cross threaded) and the second never ever is try to force it out just mess up the the treads more. Drill it out and spend some time with a hacksaw blade cutting the plug out.
I had a brain gas a while back finish tig welding a 1 inch coupler pick up the plug and threaded it by hand walked to the door when my brain kicked back in too late.
Try a Tool rental for a pipe tap use cutting oil and go easy if you going into a full coupler remember the thread goes half way Thur the coupler.
Just take it easy
Dominus Vobiscum
Swagman
