OK my tank has 3 lines coming out of it. One leads to the needle valve and on to the carb. One is the pressure line leading to the muffler. And the last is the fuel, de-fuel line. On the other side of the stopper of these lines is this:

ON the carb line is a short piece of tubing w/ the clunk. It's oriented as you said.
On the pressure line is a short piece of metal tubing that curves up towards the top of the tank.
On the fill line is a short piece of metal tubing that curves up towards the bottom of the tank.
That's why I said I need to tip the plane nose down to drain more of the fuel.

I bought the plane off E-bay. Seller said he never flown it so as far as I know it's only made two flights. When I got it I ran a tank of fuel thru it per the instructions to break in the engine. Nothing suggested a leak, but I can't guarantee that there isn't one.

I'll try to check the tank and tubing for leaks and see what happens.