Dr. Steven Novella

Because the water is filling the pipe, as the water goes over the top and then down, that creates a suction effect, right?

There's a vacuum behind the water, which sucks the water out.

It's like when you suck gasoline or water through a hose.

The siphoning.

And then, yeah, you siphon it off, you let it run.

It's the same exact thing.

So it's not just the water being forced down the pipe.

It then gets sucked down the pipe.

That's why when it all goes, not just back to the level, it all goes until it gurgles at the end, right?

Well, no, it's not really.

But it's not expanding or anything.

It's not expanding.

It's a siphon.

It is a siphon.

In that it's driven by a vacuum, sure.

Low pressure, yep.

This is the water.

So it sucks all the water out, siphons all the water down the pipe and everything with it until...

air gets, gurgles in, and that breaks the vacuum.

And then once that happens, the water settles back in, then normally functioning toilet, the water will fill up the tank and fill the bowl back up to its normal height.