This thread and a couple other older ones cite the use of Tygon for use as a stethoscope. I have to say this is one of the BEST ideas I've ever seen presented on the forum. It really works! Which was very welcoming as air leaks can be tremendously frustrating.

Together with hemostats, with tips covered in old/nitro fuel tubing you can clamp off lines and systematically find the leaks.
Here's a tip, If you have a doctor friend you may be able to get small hemostats for free. Just sterilize them thoroughly before use of course, but they work perfect for this.