what's the best way to degrease a sinking line..

This problem is generally due to grease and silicones used in fly line production, leaching though to the surface. Snowbee make a silicone solvent, which they claim "effectively removes all traces of silicone or grease from the fly line, allowing it to cut quickly through the surface film and fish as it was designed to do." Silicone removers can also be purchased from other manufacturers but personally I just wash my lines in warm soapy water( not harsh detergents)