This Thanksgiving, beware the fatberg.

It didn't sink the Titanic, but it could sink a sewer system — and you should know that before you cook that bird.

A "fatberg" is a mass of oil, fat, and grease that congeals with other non-biodegradable waste in a sewer system when people put drippings down the sink. Another, grosser way to think about it is as a football-field-size ball of used baby wipes, sanitary napkins, condoms, and other debris held together by the population's cooking fat.

And because Thanksgiving, at its essence, is a day celebrating abundance via home cooking, that means an increase in the gross stuff floating through the pipes, public sewer overflows, or backups for homeowners. Just ask the experts who see it each November.

"It may seem like the most efficient way to dispose of oil and grease is by pouring it down the drain, but these methods can wreak havoc on sewer systems," said Michael Roberti, statewide sewer production manager at New Jersey American Water.

In September, one fatberg caused 1.2 million gallons of sewage to overflow in Baltimore. That month, a 130-ton fatberg blocked part of the London sewer system — longer than the city's Tower Bridge and about the same weight as 11 double-decker buses, as The Guardian pointed out.

That 'berg took weeks to break up, with workers going at it with jets and shovels seven days a week. It had researchers looking at converting it to biodiesel and the Museum of London asking for a slice for history's sake.

The problem is much bigger than one holiday. But Thanksgiving — when cooking a turkey creates on average one cup of liquid fat, a study found — is a good time to remember not to pour fat down the sink.

"It is quite a spectacle to see dark brown tanks turn silver every Thanksgiving," Nick Hansen, a senior wastewater treatment plant operator in California, told FluksAqua, a consortium of water and wastewater professionals. "It's the turkey grease floating to the surface and the sunlight reflecting off of it."

Lucky for Philadelphia, more than half of the city's sewers are combined, meaning sanitary and stormwater sewage travel together. Those sewers are much larger, and it is more difficult for them to become blocked. But the city's smaller domestic sewers do suffer occasional grease clogs, usually related to a restaurant or other facility, said Laura Copeland, a spokeswoman for the Philadelphia Water Department.

A large blockage is rare, but could happen, she said.

"Our Sewer Maintenance Division has not seen a 'fatberg' in Philadelphia; however, we do have occasional instances where accumulation of grease has contributed to a sewer backup," Copeland said.

If they can track the grease back to a dumper, the culprit can be fined.

Grease does not break down in water, and even most soaps and other agents, like drain cleaner or detergent, can't dissolve grease effectively enough to keep the sewer system clear, according to the Philadelphia Water Department. Even if major fatbergs don't form under the streets of Philadelphia, pouring out at home can block your own pipes.

The Water Department keeps a list of sewers that have grease issues and require routine cleaning, and budgets a small amount for de-greasing chemicals each year.

Philadelphia restaurants are required to catch grease and dispose of it properly using a cooking oil disposal service; owners can be fined if dumped cooking oil is traced back to their establishment. And nationwide, publicly owned sewage treatment plants are required by the EPA Clean Water Act to control fat, oil, and grease discharges to prevent blockages.

Municipalities in neighboring counties make their own fat, oil, and grease ordinances. The substances "pose a significant threat to the Township's sanitary sewer system," Cheltenham Township tells residents on its website.

Plumbers also note that it's not just grease that causes their phones to ring off the hook after Thanksgiving. Don't force too much food down the garbage disposal at once, and don't put bones or fibrous foods like broccoli stalks or celery down the disposal, said Joseph Greenstein of Joseph's Affordable Plumbing, Heating & Drain Cleaning, which services Philadelphia and the suburbs.

"Never leave any paper towels or baby wipes in [the bathroom] because guests will tend to put them down the toilet," Greenstein said. And clear small soaps or trinkets from the back of the toilet unless you want people to knock them in and cause a plumbing headache.

Here's how to help your town avoid its own horror-movie-worthy blob (or just help your family avoid a call to the plumber):

When cooking, pour your grease, fat, and oil into a can or other receptacle. Let it cool and solidify, and then take it out with the trash. Remember also to wipe down greasy plates, pots and pans with a paper towel rather than rinsing. Don't flush fats, either; that's just as bad as pouring them down the kitchen sink.

But whether the advice will be heeded is unclear. A survey by FluksAqua found that nearly one in five Americans admitted to pouring fat, oil, and grease down the drain.

Hence the fatbergs. The term first became buzzy in 2013, when London dealt with a 15-ton fatberg. Some news clips hailed it as a new word in 2013, attributing it to the British. The word was added to the Oxford English Dictionary in 2015, along with contemporaries such as hangry and manspreading.

Other fatbergs have grown in cities including Melbourne and Cardiff. Baltimore's was blasted out using a high-pressure nozzle. The September 'berg in London was indeed turned into biodiesel and became a source of fuel.

Even fatbergs, then, can have happy endings — but throw that turkey fat in the can.