I just use the standard ol' improved clinch knot on my dropper. I think the tangle that you are describing may be the result of false casting too much with the dropper rig. The more false casts, the more likely it is that you are going ot have a mess.

That being said, I usually go one size smaller on my tippet for the dropper. Typically I will use 5x to the lead fly and then 6x off of that to a very small midge. Works alright for me most of the time.