Not sure I agree with Bob Mallard when he wrote:
"While the old school of thought was that DT lines were a good choice for economic reasons (you could turn them around when you wore out one end), that was more theory than reality. The simple fact is that by the time most anglers got around to switching them, they were too far-gone."
There is a solution:
When I began fly fishing, I didn't have much money. Both my wife and I fly fished, so it required two of every piece of equipment. One place I could save was to make my own fly rods, so I made two graphite rods from a Fenwick HMG blanks.
I also made my own WF fly lines from a single DT fly line and Cortland running fly line. It is very simple. Cut the DT fly line in half. Remove the coating from the back end with acetone and form a loop with the core by forming a loop and whip finishing it with nylon thread. Then coat the whip finish with flexible Pliobond cement.
Do the same by cutting the package of shooting fly line in half and forming a loop with it's core using the method above.
Connect the two loops and you have a home made WF fly line. You can reuse the running line and replace the section of DT fly line as it wears out.
I use Cortland 444 running line that comes in 3 diameters so you can tailor it to the Weight of DT line you are using.
Cortland 444SL Classic Running Line at BEARSDEN.COM
If you do not need two WF lines, you can keep the half section of DT line on the spool and store it in a ziplock bag for later use.
With this system, you can make the front section as long as you want. If half of a DT line is too much, keep cutting back the line until is perfect for your casting style.
It seems to me that the Welded Joint Repair
of joining two section of fly line could make 2 relatively seamless home made SF fly lines from a single DT fly line. Once you fine tune the front section of DT, you can weld the running line to make a seamless custom WF line.
The running line portion of WF fly lines rarely wear out completely. I'm thinking that the next WF fly line I throw away, I'm going to use to see if I can cut it and weld it back together. If that works, I have some DT fly line that I can measure and cut to see if I can make a welded WF line a DT adn the old WF running line.
Here's what Bruce Richards of Scientific Anglers has to say.
Double Taper Versus Weight Forward: Which is Really Better? | Fly Fishing Info Center