I keep a supply of Prather fuel line, which seems to be thin-walled enough that it will flop over inside the tank and come to the nose on downlines. For plumbing exterior to the tank, the thicker-walled varieties seem a bit more durable. Also, I believe Great Planes tanks include a length of thin-walled tubing for the clunk line. Not sure where I got the Prather, but Tower probably has it.

However, whenever I have the nose pointed down, I also have throttle at idle, and the engine should be sucking fuel slowly enough to come down without sucking dry. Seems to me a 10-second downline is rather long.