a mess looking for plug. if I could be sure trap would just twist off, Id do new pvc route. if I easily poked thru the rusted plug, the area around it must be ready to leak. 60 yrs old.
surprised someone isn't familiar with this, must be plenty of them. last 2" of trap is flared to a bigger diameter, then the bigger diameter one piece flange behind it, against finished wall. flange cant be just slipped away to see what its covering, it just spins around.
have flip phone, I take photo, try to email it and it says im not connected, other odd stuff, don't know if it can do it, reading lots of info on how, but wont work. have to have someone else check it for me to see if it can do it. started simple, but......
edit -- and that boat plug probably no good, had plumbing shop show me a rubber expansion plug, same idea, but said prob would not work. need right diameter, has to seal threads, etc...not as easy to use as a rubber freeze plug on an engine block.