Whats the name of the little tube used when trying to collect gas from a reaction?

Im not very good at wording it as a question but what it does is this. In a flask you add one of the reactants. Then you pour the other reactant in this tube that i dont know the name of, which is placed inside the flask. This means that the reactants are not yet mixed. Then you place a bung on the top with a rubber tube leading to a gas syringe to collect any gas produced from the reaction. And when you want the reaction to start you tilt the flask until the tube thingy releases all of its contents and the reaction starts. This way no gas is lost.