Knot for looping leader but to fly line
 

Set up my eight weight with a loop at the end of the fly line. What's a good knot to make a loop on the but of the mono leader? Have used a surgeons knot in the past but intends to hang in the guides. Also when you connect the sections of mono leaders what knott do you connect them with?

Google 'nail knot".... tricky to tie but when tied properly goes thru the guides fine

The nail knot is what I use to connect the fly line to 50 pd mono. At the leader end of the 50 pd mono I use a Perfection Loop. A second Perfection Loop is used to connect to 8 or 9 feet of 20 pd mono. I avoid letting the nail knot and leader get into my Guides.

If the fly line has a loop then use a perfection loop at the leader fly line connection. Most commercial leaders come with this knot. A surgeon's loop could be used but the leader will not be straight off the fly line using that knot.

If the fly line has no built in loop, nail knot (can use a double nail knot, but unnecessary) a 3” (approx) of 50# mono to fly line. At end of 3” mono tie a perfection loop, now you are ready for a loop to loop connection to leader. If leader has no loop, make one using a perfection loop. To add tippet material Should “fish end” of leader become frayed, cut off and replace using blood knot. I generally coat these knots with Loon’s Knot Sense when I’m not rigging out in the water. Good luck.

needle nail knot.

If you already have a loop on the end of your fly line use a perfection or non-slip mono loop. I prefer the non-slip mono loop for line to leader to tippet. I use 4-5 feet of 40 or 50 lb for the butt (Big Game) and about 3 feet of 17 or 20 lb Vanish Flouro for the leader.