fixing sewer cap to sewer

[brian]

Hi,

due to an extension, I am moving a downstairs toilet.
I need to close off that toilets branch connection pipe to the main stack.
I will be making a horizontal cut a few at ground level.
How should i fix the sewer cap to the branch pipe?
Is it just friction that holds it in place, or must glue be used?
I want a tight connection because the new extension will be built over this closed of pipe,

thanks,

Brian