My experience with vented loops and Irritol valves
Well, these are my observations:
1. Irritrol valves - they worked great for me. The are a very significant improvement over the stock valves while keeping the bags from filling when not in use. Currently, I am running my BIS and center locker with these valves.
2. Vented loops - while I did notice a significant decrease in the filling rate over a straight (no valve) connection when the pumps are off and filling was not desired, they still let water through. I think that in the course of 20 minutes or so, the amount of water was significant enough to turn on the drain pump. Not good enough for me. I had one of the rear lockers hooked up to the vented loop and the other one was a straight connection to the pump. Each bag had its own pump (Tsunami 800).
I am now decided to do an all Irritol (the 3/4 inch type) set up. Fortunately when I did my upgrade (went from a gravity I to IV) I run all the plumbing and electrical for the extra valves in case the vented loop thing did not work out.
I hope that helps you guys.