Equalizing Oil and Water Separation in Sample Tube

[jmstrf]

Hey guys, I posted this in a physics forum as well, I'm hoping someone can lend a hand.

My son is working on a science project, and I am stuck in trying to figure out how to help him. He's doing density testing in various liquids, and so what we started with was a small glass half full of water and half full of oil.

The glass will be replaced with a larger tank with valves etc to do sampling but the problem is this:

We would like to have the tank say the size of a beer keg, with a sample tube that is the size of a large Slurpee straw. How do we get the level of oil/water in the sample tube to match the level in the keg? When we tested this it was always the case that the water would rush in the bottom of the sample tube and fill it up, without the oil making it in.

I apologize if this sounds totally newbian, but I have looked all over for the answer to this but I am struggling to find on how to solve this, I thought maybe someone here might have an idea or push me in the right direction.

 

[BigInch]

Water is heavier than oil so it will always make up the bottom layer. If you sample from the bottom, you will never get anything other than water, until there is no more water in there. Likewise, if you sample from the top, you will never get anything but oil. You must insert the sample tube dropping it in the tank from the top, with the both the top and bottom of the sample tube open, then close the bottom of the sample tube and lift the tube out of the tank.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso