Kind of difficult getting two lines through the eye of a #18 hook :p
Truth be told I don't tie my second fly to the bend of the hook and never will. Very happy with my rig.
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It came out in another thread but there is some diagrams available on the interweb of different set-ups of the rigs.
here
Pick the knot you like and google it's tying instructions. I like what Pops said: double water knot - no problem.
Keep it simple...
If you want a quick NZ rig, but dont want to tie the dropper section to the hook bend or the eye of the hook, do a Grinner knot onto the tippet above the excisting fly, slide the dropper section, down and use the knot and fly as the stopper for the dropper section.