Presiding over a company with a market value of $143 billion apparently gives Silicon Valley's most famous billionaires a good sense of humor — and a case of corporate potty mouth.

Senior executives at Google Inc. (GOOG) launched their annual April Fools' Day prank Sunday, posting a link on the company's home page to a site offering consumers free high-speed wireless Internet through their home plumbing systems.

Code-named "Dark Porcelain," Google said its "Toilet Internet Service Provider" (TiSP) works with Microsoft Corp.'s (MSFT) new Windows Vista operating system. But sorry — septic tanks are incompatible with the system's requirements.

• Click here to read the "Dark Porcelain" press packet. May be slightly offensive to anyone no longer in third grade.

The gag included a mock press release quoting Google co-founder and president Larry Page, a step-by-step online installation manual, and a scatological selection of Frequently Asked Questions.

On some Google sites, the company's official logo — a multicolored "Google" that changes according to the season and on holidays — substituted a commode for the second "g."

"There's actually a thriving little underground community that's been studying this exact solution for a long time," Page said in the facetious statement. "And today our Toilet ISP team is pleased to be leading the way through the sewers, up out of your toilet and — splat — right onto your PC."

Marissa Mayer, a Google vice president, called TiSP a "breakthrough product, particularly for those users who, like Larry himself, do much of their best thinking in the bathroom."

[Posted on Google's Gmail Web site was another, in some ways even funnier, spoof offering: Gmail Paper, a service which offers to print out all your e-mails and sent them to you via regular mail.

"You can make us print one, one thousand, or one hundred thousand of your emails," read the phony Web page. "It's whatever seems reasonable to you."]

TiSP is the latest April Fools joke at the Mountain View, Calif.-based company, where hijinks pervade cubicles all year long.

In blogs, Google employees joke about the recent injection of green dye into milk in the cafeteria, while another talks about zany underlings filling the vice president of engineering's office with sand.

Eric Raymond, a software developer in Malvern, Pa., and author of the New Hacker's Dictionary, said TiSP nailed several important tenets of hacker humor.

The concept of free wireless access parallels a legitimate, four-year deal between Google and EarthLink Inc. (ELNK) to provide free wireless Internet service throughout San Francisco starting in early 2008.

As part of the spoof, Google said TiSP would be offered in three speeds: Trickle, The No. 2, and Royal Flush.

That's a reference to "Net Neutrality," a big political battle over tiered pricing that Google and other e-commerce companies are waging in Congress against cable and telephone companies.

"The leitmotif of hacker humor is precise reasoning from utterly bizarre premises, and once you're in that groove, you're absolutely fearless about going deeper," Raymond said. "We also have a tendency to deliberately zigzag between highly intellectual humor and utter slapstick. The more zigzags you can manage in a single spoof, the funnier it is."