Originally Posted by thekctermite
The pipe very possibly serves as a vent for other fixtures. Hard to tell without seeing a schematic of how the drainage plumbing is ran in your home.
I doubt it serves as a vent ( wet vent in this case) because if it was a "wet vent", the vented fixture would have to be on the same floor( in the basement ) as per Ontario plumbing code ( "All the fixtures must be located at the same floor." ) and there is no such extra fixture in the basement.
In the basement I only have 3 waste pipes of 3" each going vertically into the floor in different corners of the basement and this sink+washing machine.
What should I use to cap it off ( is such cap sold at Home Depot )?