Checking exhaust system for leaks

with the car running block the tail pipe (I usually use my hand real quick) if you get back pressure and can't keep it blocked - no leaks. If it is leaking, your hand will stay there with no trouble (don't linger, it gets hot pretty quick) - finding most leaks can be done by ear - get the car up on stands and roll yourself under there - verify what you hear with your hand, you'll be able to feel the "air" coming from the pipes etc. - also, if the car isn't running clean you'll find carbon stains where the leaks are