So , if this situation were in your hands you would do what?
I'd clean up the joint and resolder it with some lead-free solder. Get it to a close fit, then put some soldering flux on it and heat it at the center of the pucks and apply solder at the perimeter and wait for it to suck in by capillary action. That way, you can be sure that solder gets all the way to the center of the fitting. When I installed my new tank, I was careful not to put any side load on the nipple sticking down thru the floor.
