Identify the Problem and Old Fill Valve

What happens here

The video starts by identifying a common toilet problem: a continuously running toilet that never completely shuts off after flushing. The old-style 'ballcock' fill valve, characterized by its bulky design and float ball, is shown as the culprit. The presenter notes the rusty appearance of the old mechanism, indicating its age and wear. The goal is to replace this worn-out component with a new, more reliable Fluidmaster fill valve.

Goal: Understand the toilet malfunction and identify the existing ballcock fill valve.