Aaron McCall had fed about a dozen feet of green hose into the sanitary sewer line running from Daniel Castillo's house, blasting pressurized water toward the main city pipe, when the ground let out a deep belch.

"OK," said McCall, a city utility worker. "There, it's down."

The water that had been hovering near the top of Castillo's cleanout pipe - proof of a blockage that had backed up his bathtub for four days - dropped, and began flowing again, a scene that plays out dozens of times a week as city crews work to keep the flow going in Houston's more than 6,100-mile sanitary sewer system.

Castillo sighed. "As long as the pipe didn't burst, I'm happy," he said.

McCall shook his head. The same cold air that had given him fits starting his Pipehunter jet truck that morning, he said, likely had congealed cooking grease in Castillo's line, plugging it.

As at every house they visited that day, McCall's coworker, Frenchie Bledsoe, handed Castillo a "Grease Alert" pamphlet, part of a city public education campaign aimed at curtailing such stoppages.

The literature tells residents not to pour fats, oils or grease down the sink, but to let them cool and throw them in the trash.

Grease blockages are the main cause of Houston's epidemic of sewer overflows, a problem so widespread that it has drawn the city into negotiations with the federal Environmental Protection Agency. The multibillion-dollar enforcement action that could result - likely increasing residents' water bills - would be aimed at limiting raw sewage spills by replacing pipes and ramping up maintenance and education.

Houston, in other words, has enough sewer problems without residents making things worse.

'Flushable' items aren't

The Department of Public Works and Engineering pamphlet, for instance, also urges residents to stop flushing paper towels, baby wipes and diapers. Many "flushable" products carry that label because they won't plug a toilet, not because they won't block a city sewer pipe, Houston's wastewater division director Jason Iken said.

Any modern toilet will flush a tennis ball, for instance. But for that 2.7-inch diameter ball to avoid plugging a sewer line - most of which are 8 inches in diameter - that pipe had better be free of grease, mud and tree roots.

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The city of Houston is facing a federal mandate that is expected to require massive investments – and, likely, higher water bills – aimed at reducing sewer overflows, many of which contaminate area bayous. See which areas reported the most sewer backups in the last seven years.

That's not the half of it.

Microwaves, bowling balls, rolled up carpets, shopping carts, car bumpers, water heaters, tires, two-by-fours, hard hats, fence pipes, Beanie Babies (when those were hot) - even, city records show, "body parts" have turned up in Houston's sewers - though Iken said that last one did not ring a bell. Larger items aren't flushed, of course, Iken said, but tend to find their way into larger pipes via vandals or careless work crews.

"How many T-shirts can you flush down the toilet before the football team clogs up the sewer line?" he said, referencing an incident at a high school on the west side. "Well, the answer is 26."

Juvenile hijinks aside, Jim Thompson, regional CEO for engineering giant AECOM, said the average resident is oblivious to what happens after flushing the toilet or shutting off the faucet.

"They believe the entire infrastructure system we have, especially in the water and sewer business, is in some magic black box, that everything mysteriously works behind the curtain," Thompson said. "While I don't expect it to be understood from a technical level, I'd like to see it understood from an asset management standpoint."

Such an attitude would make residents more receptive to funding repairs, Thompson said, as well as more aware of how pipes and sewage treatment plants function.

Smallest culprits

Granted, there still are the smallest Houstonians to worry about.

"The sword for the Power Ranger, the rifle for the G.I. Joe," Iken said. "You'll find a lot of Lego parts. A lot of Barbie parts."

Anthony Williams, a 25-year sewer system veteran and now a crew supervisor, recalled one visit to a badly stopped-up home in south Houston. His crew had cleared the line and left, only to be called back days later to find the backyard again full of sewage and the homeowner irate that they had failed to fix it the first time.

Staring down the manhole as the line began to clear a second time, workers first saw rocks - the same as those being used as the man's landscaping décor. Then came the oranges - the same as those hanging on a nearby tree. Then a few G.I. Joes floated by.

Williams looked to the house, where two little boys - the eldest with more than enough strength to unscrew a cleanout cap - stood at a window.

"We were pulling them out, and the poor guy, I just felt sorry for him. He started apologizing," Williams recalled, laughing. "The kids were inside, and they knew what was going on. They started shutting the doors. You could see all the windows and all the blinds start closing."