Plumbing Question

My daughter wants to relocate her kitchen sink and it would require adding a foot to the existing copper 1-1/2" drain. It would be easier to switch the additional part to plastic but I noticed the plastic to copper adapter was labeled indicating it should only be used in the trap area ie under the sink.

Is there a reason it couldn't be used in the basement? It is in the furnace room and wouldn't ever be where it couldn't be accessed if it leaked.

I can't think of any such reason besides accessibility in case of leaks. But are you saying that you have to add a foot to the copper drain pipe in the basement, or in the kitchen? Not quite following. Also why not just add a foot of copper?

It's mostly about access as the pipe runs behind the furnace and going with new stuff lets us correct a bunch of other layout issues that waste under-sink space. It's an old house so S trap. Trying to make it neater and add a cheater vent etc.

The added pipe would be in the basement because the sink will be further away from the present location.

If you can get to the joint and monitor it, no reason not to use it there.