How to seal old drain pipe in foundation?

I have a sink in my basement that is hooked up to a 2.5" drain pipe that goes to the septic tank that is no longer used. I want to cut the pipe flush with the wall and seal it up. The pipe is probably from when the house was built in 1935. Can it be welded? If not I can cut a steel plug and epoxy it in the pipe, unless someone has a better idea.
Thanks Dante
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It matters a great deal as to what the pipe is made of and what it is doing.
It sounds like sanitary sewer, but has it been open all these years or is it plugged now? If so, how is it plugged?
It could very well be a piece of galvanized pipe threaded into a cast iron fitting. Remove galvanized nipple, replace with threaded plug.
It could be cast iron - no you wouldn't weld it. The very best would be to pop out the sanitary t and replace with straight pipe (pretty good size job)
DIY is great, but this one may be time for a plumber.
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Probably cast iron so no welding except by an expert.
Cut flush, plug with mortar or cement pre-mix. May have to add a bead of caulk around the perimeter of the plug as mortar and premix shrink slightly as it dries.
Harry K
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Dante M. Catoni wrote:

That is going to be cast iron and difficult to weld. It could be brazed, but it would be simpler to plug it this way;
Stuff some fiberglass insulation down into the pipe about 6" or so. Fill the cavity above the insulation with non shrink grout. Do whatever you want to finish off the repair, but while the grout is drying, you can slip a screw anchor into it to receive the screw for a cover plate, if you want.
Robert Allison Rimshot, Inc. Georgetown, TX
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Robert Allison wrote:

What he said... :)
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