So long as the vent line (be it to atmosphere or to muffler pressure) is the only way air can get into the tank and it goes to the bottom of the tank then it is a uniflow line. With a CL model the "bottom" of the tank is the outside wall in flight. The engine sees the end of the uniflow line as being the fuel level at all times while it's submerged regardless of how much fuel is in the tank.

RC fliers generally set up their tanks with the vent line bent up to the top of the tank. What they don't realise is that as soon as they fly inverted the vent is pointing down and submerged in the fuel and then they have a Uniflow tank all the time the model is inverted or pulling negative G. The engine then thinks the tank is nearly empty and the engine leans out .

Thanks for the info and ideas.  I am about to try the idea of pressurizing a conventional tank with a line toward the prop on the top of the fuselage and a capped bottom.  This is on another plane.

Hey Jim,  I know we are getting older, but, I remember the non-uni-flo tanks.  Like Veco and Perfect.  They would start out slightly rich and keep going leaner and leaner.  Only thing that stopped that was crank case pressure.  Have fun, DOC Holliday