Originally Posted by jester_s1

I run a T in the carb line on my gasser. There is no check valve, and the system works great. I have a filter between the T for the fill line and the carb so that no unfiltered fuel gets to the carb and I also am not putting any debris into the wrong end of the filter. There is no need for a check valve. The gas will flow in the direction that's easiest, and that's to the tank. I understand the concern that some have about putting a T fitting into your main fuel line and the possible leaks that could happen, but I'd argue that a 3 line system is more failure prone that a T setup is. I can put a zip tie on each end of my T fitting and I can inspect it easily. The same can't be said for a 3rd line going through the stopper of my tank. And I can fully defuel my tank if I want to, at least as well as the engine could do it were I just to let it sit and idle until it goes dry. But since my plane is a taidragger, I'd need to run a separate clunk for a 3 line system to get back there to where the last few drops of fuel are. What's the point in that?