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You've probably heard that it's bad to throw grease down the sink. And sure, that's in part because it can glom onto your pipes and build up over time, which can lead to long-term damage and clogs.

But the potential harm to your plumbing is nothing compared to the much bigger reason you shouldn't send oils down the drain. And by bigger, I mean a lot bigger. Like 250 meters long, 130 tons bigger.

That's the size of a fatberg that London's. Whitechapel district had in 2017. Yes, I said the word fatberg, which is a giant block of fat.

That's a thing that we as a species have to deal with now. It took engineers 9 weeks to get rid of the Whitechapel one. And fatbergs like it are continuing to grow in sewer systems around the world.

But, by understanding how and why they form, we can figure out how to stop them from sinking our infrastructure. Fatbergs are more technically known as. Fat, Oil, and Grease deposits, or FOGs, which is a less disgusting name.

And they're a huge problem worldwide. For example, the US Environmental Protection. Agency estimates that some 47% of all sewer backups in the US are caused by FOGs.

Backups are bad because they can cause sewage to leak out. And no one wants sewage in their home or in their drinking water or on their lawn or wherever else it's showing up. But preventing fatbergs from forming is a bit tricky.

You see, the problem starts because bacteria in human waste generate hydrogen sulfide - it's that lovely compound that gives rotten eggs their smell. Enough hydrogen sulfide can promote the growth of other bacteria in thick coatings called biofilms on the sewer walls. These convert H2S to sulfuric acid, which reacts with lime in the concrete to form compounds like gypsum that crack and corrode the walls.

And all of this ultimately results in the release of metallic salts like calcium sulfate into the wastewater. This is where the fat comes in. There was a lot of chemistry before the fat.

Fats contain long carbon chains called fatty acids, some of which end up loose in wastewater. These free fatty acids can react with calcium and other metals to form molecules that aren't really water soluble, so they tend to form hardened masses. This reaction is known as saponification, which fans of Fight Club might remember is the same reaction that makes soap.

So, instead of fatbergs, we could call them “soapbergs”, I guess. But that makes them sound way too good than they actually are. Since the fats generally float, this reaction largely takes place on the surface of the water, particularly where the water meets the wall.

And those corroded sewer walls, with their roughened surfaces, give the newly-formed soap a spot to clump or around. This means that FOGs typically built up in the middle of sewer walls and expand from there. All the non-biodegradable items people flush down the toilet make the problem worse.

That's because items like condoms, tampons, and so-called “flushable” wipes end up acting like glue for a giant FOG, clinging onto the solidifying mass and allowing new FOGs to start forming on their surfaces, too. But that gives us our first clue as to how to prevent fatbergs. Don't flush anything that isn't toilet paper or human waste!

I don't care if it says it's flushable. It isn't. And it's also helpful to limit the fats in wastewater in the first place.

Many people—both in residential and commercial settings—dump their used cooking oil and grease down the drain. So, stop that. Throw it away, into the trash - not down the drain.

And places that generate a lot of fatty waste — like restaurants — they should have grease traps installed. These are essentially water tanks where organic food waste settles and the fats float, so they can both be removed before entering the sewage system. Traps aren't a perfect solution, mind you — up to 15% of the fat still escapes with the water — but sewers can handle some fat.

After all, our feces contain some undigested fats—and fatbergs don't appear everywhere. They usually appear near areas with a high concentration of restaurants, like shopping malls and commercial districts. And the truth is, we might never be able to keep enough fat from entering the sewers in those areas—but there are other ways to prevent fatbergs.

Since corrosion is a key part of the problem, keeping sewers in better shape can help a lot. There are coatings that can prevent corrosion of the sewer walls, for example. And there are chemicals that can be added to wastewater that may reduce the production of sulfuric acid by inhibiting the growth of those biofilm bacteria.

But that kind of sewer maintenance isn't cheap. And it adds chemicals to the water system that could have negative downstream effects. So, unless we distribute restaurants more evenly or figure out better corrosion control techniques, there will likely be some fatbergs around.

And that means we need to figure out what to do with them when they do form. First and foremost, they have to be broken apart into removable chunks. The Whitechapel crews used pressurized water, pickaxes, and shovels to chop up that giant fatberg, for example.

And the good news about that is that while these things are pretty gross, we can get clean fuel out of them. Scientists have found that fatbergs can be converted to biodiesel, so maybe we should go down there and just mine them. One 2017 study found this could turn about 86% of the mass into high-quality diesel, which is a pretty good outcome for a nightmarish sewer clot.

But whether you can scale that into a usable process remains to be seen. And it would still be great for everyone involved, especially the people who have to remove them, to have fewer and smaller fatbergs than we do now. So we should all do our part to help prevent them by properly disposing of oil and grease, being careful about what we flush down the toilet.

If it's not toilet paper and it didn't come out of you, it probably doesn't belong in there. Because if we don't clean up our act, fatbergs will keep making a big stink. And maybe you're not the one down there cleaning them up, but somebody is.

Fatbergs aren't the only messes our modern lifestyle has created, of course. And you can hear about some more of them over on our podcast SciShow Tangents. Tangents is, again a podcast, and every week, some of the people who make SciShow and some of the other Complexly shows get together to battle for nerd cred and Hank Bucks.

It's very slightly competitive. We are trying to amaze each other with our very good science facts and our very good science poems. We try to stay on topic, but we're not super great at that, hence the name “Tangents”.

And if you liked learning about fatbergs, you'll probably love our 30th episode where we sat down with Joe Hanson from Hot Mess to talk about some of humanity's biggest messes, from fatbergs to molasses spills. You can find it all and our other episodes on your favorite podcasting platform! [♪ OUTRO].