The worst foreclosure property Mike Hendley has ever seen had 3 feet of sewage covering its basement, all of which had trickled downhill and somehow got into the house.

“You could smell it from 10 feet in front of the door,” he says.

Hendley works for the Laurel franchise of Servpro, a national company that pumps water and scours mold from flooded homes, among other services. He encountered this particular brick town house roughly a year ago, in a place he doesn’t remember exactly, “right on the edge of D.C.,” possibly District Heights.

In total, Hendley estimates that business from these foreclosure homes has picked up between 20 and 25 percent in the last year. Roughly 10 of the last 20 houses Hendley has checked out with flooding, mold, or water damage have been foreclosure properties.

“What happens is, unless you turn the water off from the street, and drain everything in the house, you’re going to have a pipe break somewhere, sometime,” he says. “And with no one being there, it floods and goes undetected, and someone comes to buy the house, and you got 3 or 4 feet of mold in the basement.”

A flooding remediation typically ranges from $5,000 to $10,000 but can creep up to $30,000, says Hendley, adding, “That’s just to restore it. That doesn’t even count putting all the drywall back together and painting it.”

Adam Bilik, who owns the Servpro in Bowie, has also seen a boost in business related to the housing bust. He says he’s done estimates for water and mold damage in about 30 foreclosure properties in the last year; he barely recalls seeing any five years ago.

A flood-damage job is an arduous, multi-step process: First the water is pumped out. Then rugs and any other unsalvageable items are carted away. Then the air is dehumidified and cleansed. The mold must be scrubbed off, mostly by hand. If the water has sat for long enough, several inches of drywall must be removed.

With foreclosure properties, the process is often more time-consuming than with your average home: “The houses that have been built through this real-estate boom are houses with bigger footprints,” Bilik says. Within his area, he sees a fair amount of older houses, likely built in the 1960s and 1970s, that are between 1,500 to 1,900 square feet, he estimates. By contrast, the foreclosure properties he’s inspected are between 3,500 and 4,500 square feet, he says.

And not everyone is willing to take the proper steps for cleanup, says appraiser Michael T. Giampa, president of Accurate Appraisal Service Inc. in Mason Neck, Va. Giampa says 75 percent of the for-sale homes he checks out are foreclosure properties-and roughly 10 percent of these have mold and flooding-related issues.

Giampa says he can smell a coverup the moment he walks into a basement. Some people just put Kilz primer toward the bottom of the wall. Others scrub down walls with water fortified with bleach to try and stop the mold. “You just can’t do that,” he says. The drywall “has to be cut out.”

And it’s not only massive floods—-the ones that turn basements into wishing wells—-that are problematic. Last week, Giampa inspected a home in Round Hill, Va., with a clogged drain that resulted in a puddle about 10 feet across, he says. The property had been uninhabited for 441 days. That amount of standing water caused mold to spread across the entire basement ceiling.

The best way to combat these problems is to winterize the property as soon as people move out, he says. But it’s not enough to turn off the water; the pipes need to be flushed out and shot through with antifreeze (Giampa recommends the pink kind used in RVs, though he doesn’t have a preferred brand). Also, he says, the electricity should be turned on to keep the sump pump running. The house should also be kept at an neutral temperature-about 72 degrees-to prevent mold growth and “funky smells.”

Fortunately, foreclosure floods usually aren’t the toughest to treat, says Servpro’s Hendley. Usually, these homes have no waterlogged books, damp couch cushions, warped wooden chairs, or wet boxes full of old school projects floating about.

“They’re emptier. They have no contents, therefore it makes it 10 times easier,” he says.

Often, people will call Hendley and ask him to check out foreclosure properties and then decide not to use his services. Instead they’ll take his quote to the bank to negotiate down the home’s value. These days, Hendley does estimates for free. Next year, no more. Today’s economy has its downside for mold remediation experts, too.

“If we run around and do 50 estimates a week,” he says, “that’s a lot of gas.”