[tomcarman]

Gary,
Probably a stupid idea on my part since I'm not a diagnostics mechanic (I can only wrench and do a bolt in replacement) but years ago I worked running HVAC equipment and natural gas lines. Upon completion of the install we pressure tested the components and looked for leaks using a simple spray bottle with liquid soap mixed up. If it bubbled there was a leak. If not, it was sealed. You could tell right away. If you plugged everything and tested for leaks this way at least you'd know if it was your install or the pressure was exiting elsewhere. Inner tubes to my way of thinking would seal quite well assuming the curvature of the membrane wouldn't interfere under compression. Getting something air tight can be quite a challenge. Give it a try, you're not out much if anything except your time.
Tom