Kohler 2705 flange replacement

[juntaka]

I have a cast iron Kohler 2705 bathroom sink and the stopper has never worked. I've removed the stopper and I want to replace the entire assembly but I can't remove the flange or the pipe it is connected too. I'm unsure if it is rusted or if the pipe screws into the sink. Anyone worked with one of these before?

Thank you!

 

[breplum]

All pop up lav drain assemblies are pretty much similar in how they go together and they don't like to come apart easily. They are all brass so it isn't rust but the flange rarely unscrews readily.
We often use mini-sawzall, which I don't recommend amateurs attempt.
maybe check youtube

 

[TomFOhio]

A picture of what you have would be helpful also.