So I want to give one of these a go. would it make sense to make one of these with a ball lock post on it? is there a good reason to push the cleaner through in the opposite direction that the beer flows?
You could, but it's not necessary IMHO. The main point is to be continually circulating the cleaner through the lines, which I think is where the garden sprayer setups fall a bit short.
I kinda prefer what I posted in the OP (natch ), as it requires that I remove the QD and clean it out, while the cleaner runs through the lines. With the ball-lock setups, I could see a possibility (which is probably small to non-existent) of gunk hiding in the QD that doesn't get cleaned out.
I think it's a good thing that I have to manually remove the QD, which ensures that it gets cleaned and another potential spoilage vector is addressed.