You do not tie it on.It slides onto the mainline and can either be left free running with a bead buffering the hook length swivel or , dependent on the design, the hooklength swivel can be pushed into the feeder itself for a bolt effect.
Under no circumstances should it be tied on as this runs the risk of creating a tether for any fish which breaks the line above the feeder.
There are sveral articles on the site on fishing the method if you do a search.