Fwiw-I was going to do the same thing thinking I could just inject fresh fluid through the drain and naturally vent the air displaced through the vent. What I found after closer observation is that the drain plug area is so tight that you're never going to be able to remove the pump hose and reinstall the drain plug without loosing more fluid than you want to and probably making a huge mess. That drain valve you posted might work depending on the length and possibly putting a 90 deg fitting on it.
What I ended up doing (posted by others) is just remove the plug and drain. 1/4" hex plug bit and drained (I also took it off the jack stands on the right side to get just a bit more fluid out). Put the plug back in and with the car on stands you can easily reach your hand on top of the PTU and remove the vent hose. I used about 2' of clear 5/16" plastic hose and dropped it down from the top of the engine bay to the PTU vent ******. Measured out the same amount of fluid that I drained and squeezed it in from the diff fluid bottle. I gave the bottle a light squeeze, removed the bottle and let it burp, and repeated 4-5 times to fill. By using clear hose, you can see any fluid in the hose from under the car and milk it in before pulling the hose off the vent ******, then I just reattached the original vent hose.
The whole process took less than an hour. At 50k miles my PTU fluid was probably close to the same viscosity as the new stuff and nothing much to speak of stuck to the drain magnet. Nothing even close to the horror stories of fluid turned to sludge some have posted, possibly due to the PP cooler.
If you click the thumbnail pic, you can see I was able to drain 12oz, the capacity is listed as 18oz. I don't have any leaks and decided to put 14oz back in. I can't say that 6 oz of the old stuff was still trapped in the PTU or if 18oz is an approximate amount that's listed in Ford PTS. I figured 2oz over wouldn't be a game ender and I think having the Temp sensor out for the refill would be the only advantage to the process listed on the Ford manual as you'd know for sure just how much to put in to the point where it weeps out. Anyone else with a PP that knows how much you were able to drain out, I'd be curious. I'll have to watch this to see how the drain valve works out.
Edit-I just poked around on the site a bit and see they offer a 1/4"-18 NPT that's less than 1" long. That may just work and they also offer a cap that would work as a secondary seal. This might be a pretty nice find on your part for all of us.
