Epoxy Butt Splice
Some may already know this one... shown to me by Tony Gades of Seattle years ago.
To join the butt section to line without the nail knot, try this EASY method that is what I believe is the best way to join the two out there.
Strip off 1/2 inch of coating from the line tip. You can dip it in nail polish remover until it gets soft enough to pull off -or- use a fine electronics wire stripper, the kind with lots of graduated wire gauges. I use the latter with success.
Then sharpen the butt mono using a fresh razor to resemble a pencil.
"Inchworm" the sharp butt inside the braided core of the fly line until it is visibly inside the exposed core -and- even inside the fly line coating. You'll see the slight bump up to the part w/ line threaded into it.
Put a drop of zap-a-gap on the exposed braided core and let dry a few minutes. It's ready to fish!
Easy! Completely compact. not even a bump thru the guides. Strong. Catches no weed or mung. Doesn't get caught on snags (sinktips). If you pull a long leader into the guides accidentally, it works it's way out easily without threading - just false cast. For the low number of times you affix a butt to line, the slightly increased effort is worth it.
Not something you'd do in the field - nail knot's quicker and easier. See the doll needle trick for a really fast approach.
Well worth the effort.