Okay thanks. I was using silicone tubing, which is looser than normal airline tubing, so that's why it was coming off so easily. I'll try removing the gasket thing.
The needle valve is part of the regulator, but it doesn't have one of those ribbed things to go into the airline.
Anyways, I switched out that last 3" section with normal airline tubing, so its fitting better.
Good call on the gasket. There's a rib after it, so after it came off, the airline is alot more secure. Thanks guys