Folks,
I bought and assembled the Tower Trainer 40. It came with a regular fuel bottle and attachments. I attached the clunk, inserted the bottle into the fuselage and assembled the rest of the plane. After running the engine to adjust the needle valve I noticed a loud rattle inside the plane. The clunk had come loose!!

This is with only running the plane statically on the ground with no flight!!

I had to remove the engine and many parts to get the tank out and sure enough, it was loose. As I examined the clunk, I found that it would pull loose easily from the fuel tubing. I went to my stash of bits and got an alternate clunk and attached it. As I pulled this clunk, it wouldn't come loose and started to stretch the tubing. This one was on solidly and I re-assembled my plane.

So ... when attaching clunks, make sure that they stretch the tubing when you give them a pull or they may come loose. I guess I was lucky to catch it before a flight.

Neil