1/2" (13mm) ball cock and float
A ballcock is a mechanism that is used for filling water tanks, much like what is sometimes found in certain toilet systems; however these are different as these are used for water tanks. They avoid overflow and in the event of low water pressure they can prevent backflow. The whole system itself consists of a valve connected to a hollow float by means of a lever which would be then mounted to the top of your tank. The float is shaped like a ball and the lever is used for cocking hence the name ball cock valve.