ORIGINAL: MinnFlyer
Rather than use a second clunk, I just bend the tube slightly so the fill/drain tube rests on the bottom of the tank. Since you don't need to empty the tank when the plane is upside-down, I don't see the need to waste another clunk.
Good idea.
It also permits you to move it as far back as possible and off to one side, to avoid possible entanglement with the main clunk.
The main clunk can't really hit the back of the tank corners, so your arrangement does permit most or all of the fuel to be drained out.