A picture is worth a bunch of words, so here is one of my currently working prototype.
It has been dosing my 100gal tank for the last 3 or 4 weeks. Weak points are the check valves. The one on top dries up a little and it takes quite some pump strength to unglue it.
I really want to try one of the other check valves, but I can't get them without incurring a $10 shipping charge, and that goes against my frugal nature. If I knew they would work I would buy a bunch to distribute the shipping cost, but I don't know that.