mbj, you're probably right. You may want to put electrical tape around any and all exposed joints as well, just to make sure they are all air-tight.

Cliff, a "test plug" has soft rubber sandwiched between two hard discs and can be expanded to seal the end of a pipe by tightening the bolt holding the hard discs together so you can "test" for leaks. You then loosen the bolt, and the plug is easily removed.