Have you ever noticed that the water in your toilet bowl sloshes around a bit when it’s windy outside?
A strong storm can even appear to ‘suck’ the water straight out of the toilet, leaving an empty basin to greet the next visitor.
There’s a surprisingly solid explanation for this bizarre phenomenon.
RELATED: Fireplaces don’t always warm your home — sometimes they do the opposite
Plumbing requires a vent for air
Indoor plumbing is one of those little perks of modern life that we take for granted. Toilets flush, sinks drain, and rarely do we ever have to think about where the water goes once it’s out of sight.
The plumbing in a typical home is called a drain-waste-vent system, connecting all your fixtures to a common sewer pipe that funnels wastewater into municipal systems or septic tanks.
This setup requires a vent to the outdoors—usually located up on the roof—that allows air to freely circulate into and out of the system.
If air couldn’t get in or out, a vacuum would form and your fixtures wouldn’t drain properly, you’d hear unsettling noises in the pipes, and sewer gasses might back up into your home.
Wind pushes and pulls air in that vent
Plumbing vents on your roof are exposed to the elements—especially on a windy day.
RELATED: Don’t fall victim to these seven dangerous tornado myths
Gusts of wind rushing over the vent pipe causes an area of low pressure to form at the tip of the vent. This suction forces air to rush up from inside the pipe, causing a noticeable pressure difference within the plumbing system.
The wind pushes and pulls on air within the pipes, sending a ripple effect through the system that’s apparent when the water in your toilet bowl starts sloshing around. Gustier winds make the effect more pronounced.
It’s a common anecdote in storm-hardened parts of the world that tornadoes and hurricanes can “suck the water right out of your toilet.” That’s partially true! Strong and persistent winds can create enough negative pressure on your plumbing system to lower the water level in the basin—and sometimes even empty the bowl completely.