Air return in the fuel system

I was just fixing my car, and have noticed, that pressure has accumulated in gas tank. However, there is small pipe that leads from the top of the gas tank to the charcoal canister at the front, and then into the air intake. Also, right where it leaves the gas tank, the pipe goes into small plastic cylinder, and then goes underneath the car, all the way to the charkoal canister. Here is my question: How does this system work, what is that little cylinder for, and can i just take it out, because it does not let any air through?