I get the type of fuel dot you put the pic up of at the LHS for about 3 or 4 bucks. They work great. I have them on all my planes. They look good & they are very easy to use. As you said with a 3 line fuel system this line is your fill & empty line. I just cut this line so that it is long enough to pull out about 3 inches or so. The plug part has a little O-ring so that when you push it back in you feel it kind of lock into place. It stays there in flight too. I have never come back down to find the fuel line dangling around the cowl. Just drill the appropiate size hole to mount the female part in the side of your cowl & feed the fuel line thru it & put your plug in. I also put a clunk on the fill line inside the tank as well as the clunk on the feed line. This makes it easier to use it to empty the tank too. I like them much better than the Dubro Kwik fill fuel valve because there is nothing to go wrong. A friend uses those Kwik fill valves & has problems with them clogging up on him. This is a simpler way to go without any problems. IMO