If the object of your quest is to avoid pulling fuel lines off to refuel here is what I have done with good results. I start with the standard two line setup; feed line with clunk and bent up brass tube for vent (presure feed from muffler). I then use a short brass tube thru the third hole in the cap; this will be the fill line. I put the fill tube at the top position of the tank cap. I then put a fuel line attached to the fill tube thru the cowl and plug it with fuel plug. To refuel I just remove the plug and pump into the tank until I see fuel start to rise in the pressure line. I turn the prop so that the pistion is near TDC and close the carb barrel; this offers resistance to fuel running into the carb. If I overfill I just hold the plane upright to drain excess fuel from the muffler.

This seems to work well, no hydra locks.