Stop flushing your tampons — they can form huge 'fatbergs' that shut off sewage

• Some people insist flushing used tampons is cleaner and kinder to fellow bathroom visitors.
• But water experts and most tampon companies plead you to toss them to spare the sewage system.

Behold the sign in nearly every public bathroom in the US: "Don't flush sanitary products down the toilet." But do they really mean it — and does that directive apply to homes?

A tampon, at least, seems like just a wad of toilet paper. Plus, flushers' argument goes, the alternative — tossing a used tampon in the trash — can subject subsequent restroom-goers and cleaning crews to a smelly, bloody mess.

Flushing is "just easier, less messy, and simply what I learned way back when, when my friends taught me how to use them in the first place," Rachel, who asked to use her first name only, told Insider.

About 57% of menstruators agree, according to one 2018 informal survey from Good Housekeeping.

But team toss maintains, among other arguments, that tampons are rough on plumbing. Why risk being responsible for an embarrassing, and potentially costly, backup?

Insider investigated the pros and cons, and talked to Bri Nakamura, an expert at the Water Environment Federation (WEF), which represents over 30,000 employees in all segments of the water industry, to set the record straight.

You should only put the 'three P's' in the toilet

Nakamura said WEF's mantra is to only flush the three P's: poop, pee, and (toilet) paper. "Anything beyond that, our sewer systems really aren't made for," she said. In addition to tampons, that includes things like hair (which can collect into a ball, blocking flow) and paper towel — even in places like stadiums where the toilets have powerful flushers.

"As soon as it's gone, people think it doesn't have an effect," but it does, Nakamura said. Non-P-materials can accumulate, leading to massive blockages sometimes called "fatbergs."

Last spring, one 300-ton fatberg, clogged London's system. "This giant mass is the result of everyone occasionally washing and flushing the wrong things down the drains, and not realising the impact that it's having," a representative for the water system told CNN.

Sanitary products were among those to blame.

The best case scenario is you have a bit of a backup

At home, flushing is ill-advised too, no matter where you live or how modern your house, Nakamura said. The best case scenario is that only your own toilet will clog.

But if the tampon continues down the line, it — along with other non-flushable materials you or housemates have flushed — can cause backup in the lateral connection, or the point at which your home's pipe meets the public sewer line.

That could be under your garden or lawn, and require uprooting and paying for it all. "People don't realize that there's something really wrong until there's sewerage in their yard," Nakamura said.

Even if a blockage doesn't happen until farther away from your home, it could cause a water main break, which can affect your quality of life (like by preventing you from using your toilet) and overall utility costs.

"Eventually it's going to catch up with utility, and they're going to have to charge customers more," Nakamura said.

There's no oversight on brands calling themselves 'flushable'

Major tampon brands indicate that they're not to be flushed, and their former "flushable" products are off the market.

And while some smaller companies insist they're toilet-safe, and flushable wipes are improving, Nakamura said there's no way of knowing just how safe such products are since there's no independent organization verifying the claims.

Don't expect toilet-safe tampons anytime soon, she added. "We still recommend just going with the three P's."