I'm in the process of stubbing out a 2" copper drain connection that will eventually service a backyard BBQ sink.

A portion of this connection will run horizontally across the base of a 10' section of patio retaining wall & flower bed, for all to see, so I figure I'll keep this part of it copper, transitioning to plastic after it's out of sight. But before it reaches the flower bed, it'll run for 10' along a side of the house where there's no access and nobody will see it.

So that brings up two questions:

(1) for the visible portion, is there a preferred lacquer or varnish treatment to keep it a "bright copper" appearance, vs. letting it weather and go green or black?
(2) for the out-of-sight portion along the side of the house, I may just paint it the house color, but what about a primer base first? I noticed our plumber installed a 2" copper vent with a coating of black something that was really hard to remove, even with sandpaper and a Dremel. Looked like flat black paint. This coating was so evenly applied that I suspect the pipe came pre-coated.

For longevity, I presume it would be prudent to use a gauge of pipe heavier than DWV for this project?