Infer the Underlying Drainage System

What happens here

The presenter explicitly states that there is a 'drainage system underneath this whole thing' which collects the water that infiltrates through the stone-filled trench. This implies the presence of a perforated pipe (like a French drain or a specific trench drain channel) installed beneath the stone layer. This pipe then carries the collected water to an exit point, which is vaguely indicated as 'somewhere out there' off-camera. This underground system is crucial for efficiently moving large volumes of water away from the hardscaped area and preventing oversaturation of the underlying soil.

Goal: Understand the hidden components and overall functionality of the drainage solution