Good afternoon,

Electrician by trade. Over the last month or so I experienced the smell of sewer gas and a small leak under the carpet in the basement. Only happens when the washer is on. Pulled up the carpeting and found what appears to be a 2" line with duct tape cut flush to the floor. Moist during the washing cycle along with the odor. Dissipates and dries out after laundry. I would assume its an abandoned line. Should I just chop out and seal with a jim cap? Any thoughts?
Thanks, Rich

That is probably a floor drain, no longer used because of the carpet. Don't know what a jim cap is. Since what you see is probably the trap and floor drain fitting any regular pipe plugs are not likely to fit. Stuff with newspaper to within 1/2" of top. Pour a little concrete in to seal. Can be easily remove later on if necessary.
The presents of moisture indicates a partially blocked drain line between the washer stand pipe and the main drain causing a back flow to the floor drain.
Snake washer stand pipe to main drain.

Before you start to cap any lines off, you should first know what they are.
Harold suspects a unused floor drain. You should pull the carpet and look for one.
I if the water is coming from there. Then you have a partial blockage in the main.
Checked further and let us know what you find. Good luck, Tom

If it is a floor drain you should be able to pour a half-gallon of water into the pipe and afterwards look into the pipe and see standing water. Otherwise, capping with a jim-cap or an expanding plug (see image) will work fine as a temporary fix. For as permanent fix, you chip up the floor around the pipe a little and install a shielded clamp and a schedule 40 cap (heavy cap).

Mark