Jon is correct. Tighten the nut until it bottoms out. If this causes the tailwheel fork to bind, then something is amiss.
When the nut is tightened down all the way, the system is designed to have some clearance so that the parts can swivel properly.
If you're not tightening that nut down all the way, depending on the nyloc to hold the nut in just the right spot, you've got something amiss. Fix it.