I have a Keeprite furnace. There is a small plastic pipe 3/4 inch that runs from the furnace
Into a 'cylinder' before going into the drain in the basement floor. The cylinder has now turned black inside. My questions are

1. What is this? Is it to do with condensation?

2. Should the 'cylinder' be replaced, if so. Whom do I get to replace and what would be the approx. cost?

The cylinder might be for corrosion chemicals that are used with some high efficiency units to prevent drain pipe damage. Post a picture so we can see what you have. Brand and Exact model of furnace also.