The way the sewer cleaning firms do it around here looks scary
but it works. Those large threaded plugs are usually brass.
They pound the edge with a cold chisel and hammer, until they
can remove it. It won't be reusable, of course. Then they
replace it with a plastic plug, which will come out much easier
next time.

Don't get too attached to the old brass plug. Pound away.

Bruce Ferguson wrote:
I apoloigize ahead of time for this off topic post but I figured with all
the people out there some one may have the answer.

My house was buildt in the 50's and has the iron sewer pipes under the
house. The cleanouts look like a two piece afair. The first is a tapered
piece that is held in with picking or lead and the screw out piece is in the
middle. Of course they are all frozen and stuck. Question, do you think
heat would help free them??? If so would you heat the center piece or the
piece it screws into??? I don't know if they make those pieces any more to
dig out the packing and replace them. Most everything is plastic. I guess
you can figure out why I need to get to the clean out. If some one knows a
web site I would be happy to go there.
Sorry again for the off topic post.

Bruce