How to siphon gas

HOW TO SIPHON GASOLINE (OR ANY OTHER FLUID) WITHOUT GETTING A MOUTHFUL

It never fails. Time to cut the grass, storm is moving in and you don't have enough gas in the can to fill the lawn mower. Ah haaaaa, a simple solution, I'll just steal a gallon from the wife's car. She'll never notice it's missing.

Get a length of tubing - stick it in the tank - bring the can over near you and start sucking. Ptoooooie! Yuck, damn that gas tastes awful!

Cut to the chase . . . .

How many times has that happened to you? Well here' the scoop on how to siphon any liquid from any container without even getting close to getting a mouthful. Which could lead you to frustration and rage and before you know it your car is listed in the local car classifieds.

First, let's talk a bit about liquid and levels and gravity. You might have heard the saying that a liquid always seeks its own level. What that means is if you put a gallon of water in a pail you will expect it to be at the same level all over the surface of the pail. Even if you insert a baffle in the pail to split it into two halves of a pail you would expect that some of the water would seep around or under the baffle and come to the same level on both sides of the baffle.

Now it's time to expand your thinking. Let's take a pail and make provisions to attach a hose to the bottom of the pail on a nipple. Make sure the free end of the hose is not lower than the top of the pail and fill the pail half full of water. No water runs out of the end of the hose because the open end of the hose is higher than the water level. However, if you move the end of the hose lower than the water surface in the pail, water will flow out then. This is true even if the hose is twenty feet long and the end is in another room! The water has a continuous uninterrupted path from the pail through the nipple through the hose into the other room. Ok, we all agree?

Now the secret in the last paragraph is a "continuous uninterrupted path". Let's see what that means. Take another bucket and a five foot length of clear plastic hose. I want to use clear hose so we can see whether or not there is any air in the hose. Fill large glass container, like a bowl, with water. Take the hose to the sink and carefully fill the hose completely with water. You can do this by letting the hose droop into a "U" shape and by holding the ends of the hose at the same level while filling the hose from the faucet. Got the picture? OK, now carefully bring the hose to the table with the glass container of water on it. Put one thumb on each end of the hose, submerge one end of the hose completely under the surface of the water and remove that thumb. Make sure you have no air in the hose (that's why it is clear plastic). Now carefully let the hose droop over the side of the table, keeping your finger on the other end of the hose.

If you now bring the end of the hose with your thumb on it to a point higher than the top of the glass container and release it you will see see something amazing. Because the water has a "continuous uninterrupted" path from the inside of the pail and over the edge of the pail through the hose, the water in the hose will seek its own level! If you put the hose near the glass bowl and sight through the hose and into the glass bowl you will see that the water level in the hose is precisely the same level as that in the glass pot! It ain't magic. It ain't rocket science. It's nature!!

On with the siphon demonstration. Now comes the fun. Get another container and put it on the floor near the table. Slowly lower the open end of the hose until the end of it is just at the level of the water in the glass container. Now lower it one more inch and make sure the container on the floor is underneath. Water freely flows out of the open of the hose. How long will it flow? Until the level in the glass container drops one inch! The water has once again sought its own level. And you have just seen a siphon in action! That's all there is to it.

So let's see how we can apply this to starting a siphon - without getting a mouthful of water (or gas). The secret is to somehow get one end of the hose well below the level of the liquid in the tank from which we wish to transfer the fluid. So take the hose, empty it by just lifting the end way up in the air and let the water run back into the glass container. Now stand on a chair so that you are well above the table and the glass container. Stick one end of the hose in the glass container well below the surface of the water. Now, carefully suck on the other end of the hose and watch the water level rise in the hose. Keep sucking until the water is about a foot from your mouth. While still maintaining suction, carefully bend over so that the hose can droop over the end of the glass container and form a loop which droops down to the table top. Slowly release the suction and watch the water level drop. How far will it drop? Until it reaches the level of the water inside the bucket. But since you have a loop of hose drooped over the edge of the container there is still water in the hose, right? Now lower the free end of the hose to the floor and stick it in the container on the floor. Water will flow out of the end of the hose and continue until the container on the table is empty, assuming that the hose goes to the bottom of the container. That is a siphon. You started it without getting any fluid in your mouth.

So, here's how you apply the principles we just learned to siphoning gas from a tank and into a container so that you can get the lawn cut and stop fooling around with glass containers and tables and water!

First, make sure you have a sufficient length of hose. That usually means six feet or so. I use 3/8 inch clear Tygon tubing so I can see what's happening. Push the hose into the gas tank until it is below the surface of the gas in the tank. If your wife is any thing like mine, that means you have to push a few feet into the tank! Make sure the end is under the surface by blowing into the hose and listening for a bubbling noise in the tank.

Now, from what we learned before, make a long loop of hose such that it goes clear down to the ground and comes back up to a point well above the fuel level in the tank. If you have to stand on a chair to get sufficiently above the gas level, do it! Now suck! Watch as the gas comes up into the hose and starts to flow down the loop towards the ground. It will then start to fill the hose until the gas in the hose reaches the level of the gas in the tank. If you keep the free end of the hose high enough nothing will ever come out. if your stick the free end into a can and lower the free end and the can towards the ground you will see gas flowing into the can. When you feel that you have enough gas in the can to fill the lawn mower simply raise the hose and the can above the level of the gas in the tank and the gas will stop flowing. If you leave the hose in the can, submerged below the surface, gas will start to flow back into the gas tank of the car!

When you are finished, just lift the free end of the hose way up high and let the hose empty back into the car tank, yank it out of the tank and go cut the grass!

Back to Brother Bob's Home Page