Joe,
What stops fuel from flowing into the carb with that "miracle fueler"? Sure the "Y" should reduce that, but it probably won't prevent it entirely. Just playing devil's advocate here.

I've never had a problem with a dot coming loose, but have had a couple that were a bit tight.

Righty,
If you're concerned about fuel flowing into the muffler during re-fueling with the set up in your diagram, you could always put a check valve in the line to the muffler (after the "T").
Dennis-