Sink tips or full sink? What rate or sink (usually measured by ips or maybe "type" or both)? Sink tips are generally used to swing flies (streamers, wets, nymphs) in moving water, and full sink lines are used in still water. Somewhat interchangeable, but a sink tip mends more easily in current than a full sink, and a full sink gets down and stays down better than a sink tip in still water. Both are easier to cast than a floating line with weight, and they are therefore useful for getting unweighted or lightly weighted flies down to fishing depth.