Adjust Water Level and Test Flush

What happens here

With the tank filled, check the water level. The optimal water level should reach the 'waterline' mark indicated on the flush valve canister inside the tank, or about a quarter-inch below the overflow tube. If the water level is too low or too high, adjust the fill valve by rotating its top section. The presenter notes the initial adjustment isn't quite right, requiring a slight upward adjustment of the fill valve arm to raise the water level. Flush the toilet to confirm proper operation and water level after adjustment.

Goal: Achieve the correct water level and confirm proper flush function.