A federal court case could give new meaning to "Don't mess with Texas."

Two portable toilet vendors are engaged in a trademark dispute over using the state's outline and Lone Star to adorn their outdoor loos. Texas Outhouse of Houston, which trademarked its version of Texas-and-star earlier this year, has sued rival Texas Waste, claiming the Alvin company's use of similar images has diluted Texas Outhouse's "iconic" brand, making it difficult for users to distinguish portable toilets and suggesting that the al fresco powder rooms are the same.

It's an argument that legal specialists say may not pass the smell test. Practically speaking, said John Keville, an intellectual property lawyer at the Houston law firm Winston & Strawn, logos -- iconic or otherwise -- don't matter when you gotta go. "Texas Waste will probably flush that famous mark and dilution claims pretty quickly," Keville said.

Texas Outhouse was founded in 1994, building a clientele among construction companies, local sport franchises and public festivals through word-of -- well let's just say user experience. In 2008, the company which is one of the bigger players in the local market, adopted its logo, registering it with the U.S. Patent and Trademark Office in January, according to the lawsuit, filed in May in U.S. District Court in Houston.

Rodney L. Drinnon, the lawyer representing Texas Outhouse, said the portable potty business is fiercely competitive in the Houston area, where at least 10 companies battle to put fannies in the seats. Texas Outhouse has become "locally famous," according to the lawsuit, its products recognizable, not only by the Texas logos adorning the fronts and the sides of units, but also their beige color scheme, highlighted by green doors.

In addition to adopting a similar logo, the lawsuit alleges, Texas Waste, formerly known as Fresh Can, changed the color of its units from bright blue to tan to benefit from Texas Outhouse's reputation for "high quality portable waste management," the lawsuit alleges. Texas Outhouse is asking the court to prevent its competitor from using an outline of Texas and star on its toilets and marketing materials.

"It's all about protecting the goodwill Texas Outhouse has built over the years," said Drinnon.

Travis Vargo, a Houston lawyer representing the Texas Waste Co., said he only got wind of the dispute after Texas Outhouse filed its lawsuit. He said the companies are trying to settle their differences out of court, but expressed surprise that anyone else would care.

"Who knew poop could be sexy?" he said.

If the case goes to trial, legal experts said, the outcome will likely depend upon the opinions of frequent outdoor toilet renters -construction companies, sporting events and festivals - to determine whether there is brand confusion among customers.

In Bellaire, where the construction company Joslin is installing underground pipes at the new Evelyn's Park, site superintendent Christopher Dean said the freshness date rather than the logo determines which portable toilet workers use. The longer a unit has stayed on site, he said, the less likely it will be a top choice.

Collin Dacus, the assistant superintendent, says that when he shows up at construction sites and sees portable toilets, he never says to himself: "Yeah, this is going to be good." Given the choice between different brands of portable toilets, he said, he'll head to a nearby gas station.

Texas Outhouse v. Texas Waste is not the first tussle over the use of the Lone Star in company logos, said Jane Langdell Robinson, who handles copyright issues at Ahmad, Zavitsanos, Anaipakos, Alavi & Mensing in Houston. In 2010, in a case involving two self-storage companies, the U.S. Court of Appeals ruled that the iconic image of Texas is not inherently distinctive and can't be legally protected as a trademark. She said she expects the courts would have a similar view of using an outline of state.

Jacqueline Lipton, a law professor and codirector of the Institute for Intellectual Property and Information Law at the University of Houston Law Center said the case will come down to two issues: Whether there a protected trademark and whether customers are likely to be confused by the similarities of the logos. As she delved into the doctrines of intellectual property law, she stopped herself for a moment: "I can't believe I'm talking about outhouses."