Presuming the tank is correctly set up, the clunk (the metal fitting on the end of the fuel supply line) will drop to the front/bottom of the tank, and remain in the fuel.

Essentially, again if the tank is set up correctly, the clunk is "free"...that is to say, it can rattle around anywhere in the tank it needs to. As a result, no matter how the tank is tipped, the clunk falls to the lowest point...exactly where the fuel is.

One of the common problems with tank setup is cutting the supply line too long. As a result, the clunk either gets wedged against the back of the tank, or the line is too long to allow the clunk to "bend" it, and fall to the front. This sounds like a likely suspect for the issue you describe.

When setting up a tank, cut the line so that, if held "upright"...that is, with the plug at the top...the clunk will dangle about half an inch off the "bottom" (the back if the tank is mounted flat) of the tank.

Here in a moment, i'll make up a couple drawings to indicate what I mean.