|Here's the problem. If you never been spooled by a leviathan, I can guarantee you when it happens, you will wish you had spooled your reel to maximize every bit of your reel spool without leaving ANY short amount of excess on the filler spool.
When a fish has you to the bottom of your spool, you will wish that 1/4" gap that you missed when filling your reel was just a bad dream. On the other hand, over-filling your reel creates its own set of wasteful problems. As well, the stuff is expensive. So leaving a short amount on the filler spool is a waste.
To get it perfectly on your reel is a bit time consuming, painful in the arms, and mundane. But, you only have to once in every great while. I have two original Avet LX (circa 2002 or 03) that still has the original 65# Power Pro. I would take those two reels out tomorrow to target sturgeon; that's how much confidence in line that's at least 10 years old!
It's a three step process using two spare reels and their drag system. . The spare reels must be larger in capacity than the targeted reel.
First, mount the targeted reel to a rod, thread the braid the guides, and temporarily attached the it to the bare spool using tape.
Without tension, reel up the braid, attach the mono backing, fill it to the very top of the fill line of the reel (Hint: based on line diameter, the braid filler spool should never be longer than the reel capacity. Also, the mono backing strength should be equal or greater than the braid).
Remove the targeted reel from the rod and mount the first of two transfer reels. Re-thread the line and again attach via tape. This time, add tension by backing off the drag from the target reel and transfer the line.
(Hint: Using heavy boat rods will stabilize the reels during the transfer, as well as add tension to the line during the packing of the spool).
Repeat the above step for the second transfer reel. Maintain the tension during the transfer. Note: with this step, the mono backing is staged to be on the bottom of targeted reel's spool.
Final step - transfer the line back to the originally targeted reel. Make sure you use a good knot mounting the mono backing to the spool.
A jerk on one end of a line waiting for a jerk from the other