hello on ocasion I would notice a long stream of fuel exiting my plane, at the time , was just running the vent from the tanl down to the bottom of the plane. Got to thinking about this problem, oil residue on the bottom of the plane, so I now run the vent to the very back ,and low point of the fuselage . Problem solved, no more oil residue on the bottom, and if I want to tilt the plane up on its nose, the vent line does not have to be clamped. This little idea has worked on all sizes of giant scale planes I fly, from 2.5 c i to 11.6 c i engines. I use a nylon tube from near the overflow vent and a piece of fuel line to the nylon tubing., Usually try to exit as far aft as possible. Give this a try, I think you will like it. regards jack