It was time to climb back up the hole. The burly white-suited engineer checking the vapor measurements didn't like the readings he was getting. Growing impatient, he seemed to be having a tough time grasping why an American film crew had traveled 5,000 miles from home to stand calf-deep in a steady stream of human excrement. He wasn't the only one puzzled.

We'd come to Bochum, Germany -- or rather, its underground sewer system -- to check out one of the more malodorous tax shelters U.S. corporations are now using to cut their tax rates. After suiting up in white coveralls and heavy rubber boots, we'd climbed down through an open manhole into the dark stench-filled tunnel. The system's technical manager was pointing to various piping that had been leased last year by a big U.S corporation. But my feet were cold and I kept wondering why anyone would want anything to do with what we were standing in.

The answer, of course, was money. Big money. By leasing Bochum's sewer pipes a U.S. company was getting a big tax break. It's called cross-border leasing, and since the mid-1990s it's become a huge business -- with more than $100 billion in deals in Germany alone over the past five years. The leasing industry is quick to point out that there's nothing unusual about cross-border leasing. Leasing is just another way of financing business. But down in the Bochum sewer it was tough to see any business taking place. The sewer pipes had long ago been built. The city still owned and operated the system. The complicated leasing deal -- the U.S. investor leased the sewer pipes and Bochum leased them right back -- hadn't really changing anything except the bottom line of the U.S. investor's tax return.

We knew that foreign municipalities were getting millions of dollars for agreeing to lease their city assets to U.S. companies, so we had stopped by Bochum's town hall to talk with officials who cut the deal. Our German field producer, Jochen Bulow, tried repeatedly to line up an interview with Bochum's treasurer. But she had become a candidate for mayor, and it quickly became apparent that she didn't want anything to do with publicity about the leasing deal. Cross-border leasing had become a hot political controversy in Germany.

Last February, Bochum's consideration of the sewer lease ignited a local firestorm as opponents rallied support for a petition that could have scuttled the deal. The local tenants association didn't see the city's payoff -- expected to be $20 million -- reducing residential sewage rates. Local Greens saw evil in unchecked globalization. Together, the forces mustered more than 14,000 signatures opposing the deal -- enough, some argued, to derail the contract. But Bochum's city council forged forward anyway, and the lease was signed.

Yet many details of the deal remained shrouded in secrecy. Like most cross-border contracts, the size of the Bochum lease and the identity of the U.S. investor were kept confidential. Vice-Mayor Gabrielle Reidl told us that the U.S. investor had insisted on secrecy. But through other sources we confirmed that the Bochum sewer lease was a half-billion dollar deal involving the fifth largest U.S. bank -- Wachovia. (Last year, Wachovia's annual report indicated that it paid no federal taxes on $3.6 billion in profits. A big chunk of its tax savings came from its $3 billion in leasing activities -- though how much was generated from cross-border deals like Bochum's is impossible to tell.)

After climbing up out of the sewer, we stripped off our coveralls and took in the welcome fresh air. An older woman, curious about our cameras, stopped to vent her dismay about the sewer lease, fearful that Germany was turning over more and more of its public assets to big American corporations. She was quite angry about it all. I was struck that German citizens who were getting millions of dollars from U.S. taxpayers -- a gift from the American taxation system, as one German official put it -- were the ones up in arms about the cross-border leasing business. Those of us picking up the tab -- you and me -- have had little to say about the billions in questionable corporate tax breaks. Maybe that explains why the U.S. companies are so keen on keeping these deals underground.

Rick Young is the producer and director of "Tax Me If You Can."