Happy to help. There really are zero resources on the web for this. And everyone I asked for advice kept insisting "switch to abs" - well as you can see (literally) this is not challenging, cheap (free if you have a decent torch), and takes next to no time to complete.

Bless your heart! I had a copper flange on 3" copper pipe. It took a little patience to get enough heat into the copper, but off it came! Thank you! Thank you!

I thought mine was dry fit, so I've been beating on it with a hammer while prying upward with crow bars. I even stuffed a 45 lb. free weight bar into my 3" copper pipe to give the copper pipe counter weight while I beat on the flange. Finally I came to youtube to figure out why it was so stuck. Oh. I see. Time to go buy a torch.

@OxenHandler - wasn't worried about igniting the wood, as long as you don't subject the wood to continuous flame it shouldn't ignite, if you are concerned about igniting wood while soldering you can always use some tin foil to deflect the flames. - since there was nothing wrong with the existing flange and since you can't get any better than brass, i just cleaned it up, polished it and re-used it. - and as for lowering - tile the floor, set flange on top, re-solder.

I had this exact same problem! 70s-era home with ALL copper pipes, including vents. Could not find anywhere how to remove copper flange. Bought MAPP cylinder and used it to heat up the entire flange area. Eventually all the flux melted out of the joint and I was able to pry up the old flange. Be sure to wear a mask and try to ventilate the area. The burning flux created quite a lot of smoke in my upper-story house. The relief of getting it off was well worth the effort!

I have the same on my bathroom I didn't know what to do. Thank you now I can do it first i was thinking to cut the drain lol you're a savior thank you sir

@OxenHandler Not certain to be honest, I only have experience with solder, and it looked the same... I used solder to re-attached it. I thought oakum and lead was for cast iron fittings....

Niiiice! :) Thanks for posting this!! I'm now like you were then... LOOKING for info online as to how to unsweat 3" copper... I feel like I'm in the desert of nothingness :P Then, wallah, YOU, actually DOING it! You rock, man! ;-) Gotta unsweat a screw type cleanout cap fitting from my main sewer line where the main line leaves the house in the basement (it's underground about 6 inches, but dug up right now) so I can add a new 3" line at that point for the new basement bathroom I'm putting in.

Thanks for the video. Did you have to cut the copper pipe to lower the flange when you reattached it? If so, how did you go about doing that?

I used a bolt cutter and broke the flange, It was much easier than torching it.

My question is what did you do to install a new flange? I can't find anything about replacing the flange on a copper drain. I am thinking about trying a push to fit flange but idk if it will fit? Any help appreciated.

Shit that's what I'm going to have to do with mine. At least I know how I guess.