On the subject of clunks and gas fuel lines, I saw first hand yesterday a tygon fuel line that had been left in a tank for about 1 year.
The flyer had a DA-50 on a 28% plane. The engine almost stalled out a couple of times and would have been potentially fatal.
When we examined the fuel tank, you could not hear the clunk when shaking the tank. Upon opening the tank and examining the tygon tubing, the fuel pick up line was so rigid it would not move.

Can anyone comment on the length of time that tygon tubing should be replaced and/or a better type of fuel tubing to use inside the gas tank?

Jaketab