How to Tie a surgeon's knot when fly fishing
To add tippet to your leader, overlap a piece of tippet by no more than six to 8 inches with the end of the leader. Make a double overhand knot in the middle of the overlapped pieces, being sure to pass both the end of the leader and the entire tippet twice through the loop. When you tighten, lubricate the knot and pull on all four ends at the same time. This is crucial for maximum knot strength. This knot is so easy that I usually tie it as a triple overhand for a little extra strength. This is particularly helpful if your tippet is a different brand than your leader.