Tapping & Dressing Hydrant
In this clip you see the engineer carry the "hydrant bag" (with tools and adapters) to the hydrant, stretch the intake line, and "tap" the hydrant.
First the hydrant is flushed to remove any debris from the hydrant barrel. Sometimes there are debris is fire hydrants from the water main or from people placing objects inside. These debris can damage the pump on a fire engine.
Second, in no particular order, a gate valve is placed on a secondary discharge of the hydrant and the large diameter feed line is attached. The gate valve is in place for an additional water source that can be established without first turning the hydrant off.
Lastly, the hydrant is turned on and water is fed into the engine to fill the tank and feed the attack lines directly.