Siphoning: The Emergency Pump

Fluid being siphoned between beakers.
There may be times when you find yourself needing to transfer some sort of liquid from one container to another but can’t pour it and don’t have any mechanical pump you have another option and it only requires a hose. It’s called siphoning and it’s really easy.

The Method

Position the opening of the full container above the opening of the empty container and put one end of the hose as far into the full container as you can. Next, suck the air out of the hose until the liquid starts flowing out, then immediately place that end of the hose into the empty container. To stop the flow you just need to pull the hose out of the full container. 

You can use your mouth to suck the air out, but this can be dangerous. Even if you’re very quick to spit it out you’ll likely swallow some or absorb some through your mouth, so if the liquid is in any way toxic it could have serious health risks. A much safer option is to use a siphon hose, which has some kind of pump on one end to suck the air out. 

If you can’t get the full container above the empty one, you’ll need some sort of intermediary container. 

The Science Behind It

Siphoning actually works on partially the same principle as drinking through a straw. When you suck on a straw you reduce the pressure inside. The universe doesn’t “like” this new pressure differential so the atmospheric pressure around you forces the drink up the straw. As long as you keep sucking the flow up the straw continues so no pressure differential ever appears. Siphoning works the same way except that once the flow starts it’s maintained by gravity rather than suction. 


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