The tank is 5252 aluminum. The port I'm tapping into had a copper stud about 4" long brazed onto a copper elbow. Nordic says they use a SS bushing at all tank fittings to isolate the tank from dissimilar metals. Mine shows no signs of electrolysis after 22 years so I'll re-use the SS bushing to isolate the tank from the new copper pick up tube. Thanks Maine Sail, that pex and aluminum does sound like a good alternative but I think this will be OK too.

Max