Water Softener Drain Line with Loop - Flexible PVC to Sharkbite?
If you use flexible hose, and take the sharkbite fitting off the drain, the flexible hose will/should clamp right onto the 1/2 inch copper pipe. Or, you (or a plumber if you don't solder as I might expect for sharkbites) can solder a brass/bronze barbed fitting there, or I suppose you can build some sharkbite contraption that ends in a barbed fitting. 

Hint, use enough hose onto the pipe to allow placing TWO hose clamps on the pipe, and put the screw-clamp part on opposite sides.

Alternatively, you could investigate what sort of threads you get if you unscrew the plastic barbed fitting, and look for a PEX fitting that matches that thread.