The other day I was asked by a fellow angler whom I had seen on the river in the past about what sink tip line I recommended for fly fishing for the chum salmon. Usually we are fly fishing in just 3ft of water that isn't moving too fast (chum hold in slower water). I told him that I preferred to use the Type III sink tip lines and a leader not more than 3.5-4ft. Heavier lines tend to snag too many fish or too much bottom and casting 45 degrees downstream helps prevent both snagging bottom and fish.
With that information he began to change his sink tip line. I noticed that when he was switching his sink tip to something lighter he made a common error. He put the loop of the sink tip through the loop of the fly line and then put the tip of the sink tip line through itself. Putting a sink tip on that way will result in the line cutting into itself under tension especially with a big chum on!
Here is a bit of instruction and a short video I took to show how to properly put the loops together.
Step 1. Put the loop of the fly line through the loop of the sink tip.
Step 2. Put the end of the sinking tip though to loop of the fly line
Step 3. Pull the sink tip through the loop of the fly line until it forms a square knot (reef knot).
The reef knot does not allow the line to cut into itself. That is when you know you have done it right!
Good luck out there, those chums are strong!