I like the last version! I was going to make something just like this to remove solids from my AP system. I saw a guy using a filter like this with his system and it looked like it worked very well. Ended up I didn't need it, but I sure was intrigued. I have a couple of questions, is the GW coming in from a higher point than the filter? What is the function of the last reservoir with the bell siphon?
Oh, in case you haven't yet worked with these, I'd highly recommend Uniseals for connecting the pvc to the barrels instead of bulkheads. They are so easy to use, you just drill the hole, put them in and stick the pvc through (although that can be tough at times). They're designed for connecting pvc to curved surfaces and they never leak. They work with any wall 1/2" thick or thinner.