Make up a batch of net dip to tar that mainline.
Lowe's or Home depot has the materials needed.
Here's the recipe, use it to dip netting, line, decoy cord, use it as a wood preservative/stain, and makes a dandy dessert topping,
, it will dry and not tar up your hands, and will darken (brownish black), and stiffen your lines.
1 gallon can non-fibered foundation coat,
1 -2 gallons of mineral spirits (paint thinner)
In a Spackle bucket add a quart or so of the asphalt, depending on how much finished product you want, and about a gallon of thinners, roughly 1 to 4 ratio. Stir well, the blacker it is the more asphalt is in it, more thinners and it gets more brown. Dip a sample of your material and see how it looks, the more thinners the faster it dries, see if it gives you the desired effect. This ain't the culinary institute, the recipe is a work in progress, thicker/thinner, browner/blacker, it's up to you.
Dip your coiled line and hang to dry, over the bucket is good to catch the drips, remember the wood staining ability? It should dry over night or a day or two depending on temperature, humidity, and how thin you made it.
You might want to wear gloves and old clothes when you do this, it dyes new jeans and leather shoes too. lol.
Cap the bucket and save for the next dipping victim, it lasts forever, you just might need to add some more thinners if it gets too thick.
Good luck, If you use it, let me know how it worked for you.