Thanks again to everyone who chimed in with suggestions on gear for trolling lead core. Now for a different question. What is the best knot for lead core? How about for tying to the backing, line to line or swivel?

you can tie a blood knot.
45# test lead is about the same diameter as 60# test leader material, so it makes a nice blood knot.
you can also splice it. bye taking out about three feet of lead, insert the mono, then wrap the end with floss, and plyobond the connection.