It depends on the reel but try this.Put your reel on the rod.Thread through the eyes.Tie on the line to the spool using a grinner.Put the spool in a bucket of tepid water and wind on keeping even pressure on the line as you do so.You can use the butt section alone.Some reels are just not suited to our method of filling spools to the brim.Americans who use fixed spools for spinning do not tend to fill spools to the brim and long casting and line lay are alien to them.Shimano seaspin type baitrunners are a classic example.Hope this helps
I put the spool in a bucket and then run the line through the middle of the Yellow pages.
I find this gives enough tension for lines upto say 8lb, anything above that and I normally put a couple of 2lb leads on top of the book.