About this time last year I made something similar under the "use what you got" principle. I cobbled it together from an empty OJ bottle, a schreader tire stem valve, a 3/8 ball valve, a 1/4 flare fitting, and a MIP reducer fitting.
It worked kind of OK, but required CO2 pressure to push the cleaning solution, needing me to change to a tire filler fitting on the end of my CO2 line from the regulator (a real PITA), and to hold it upside down to dispense the cleaner while adding CO2 with the other hand (another PITA). Also, because it attached to the flare nut on the beer line, it didn't clean the liquid ball lock fitting. It leaked a little too because the bottle wall is so thin and hard to seal well without tearing. So in the end, although it cleaned the lines just fine, I didn't like it all that much and really didn't like getting the caustic solution dripping and leaking on my hands.
So I finally broke down and built one of the pumps of the OP's original design. I have to say it's great device and 100% better than my junk. All the thread size banter aside, it goes together great if you follow the directions. I did do a couple of things slightly differently though. I puchased the Firestone ball lock post with the right thread, a "universal" poppet valve (see pic), and flare/FIP adapter from the same LHBS and HD as day_tippr. When I started putting it together I didn't like the amount of teflon tape it seemed to need to seal. So instead, I again used a couple of parts I had on hand to make better seals. I took off all the teflon tape and added a #10 o-ring (Danco brand at HD - see pic) to seal the flare to the ball lock post. For the adapter to the plastic pump head I took off most of the teflon tape leaving 1 wrap to keep the brass from galling the plastic treads and added a 1/4L sized faucet seat washer (Danco brand at HD - see pic) inside the brass adapter to funtion as a gasket. I had to sand down the OD of the faucet washer just a little, to the edge of the "1/4L" marking on the washer using some med. grit sandpaper on a sanding block, to get it to fit just right. These small changes should make it very reliable and 100% leak proof. My hands will like that!
I used it the other day and it SEALS GREAT and WORKS GREAT too! Kudos to the OP for posting this.