You throw your garbage in the trash can and later the garbage collector comes and picks it up.

When you throw the trash in, it flies into an underground hopper.

Next to the funnel is a redstone comparator that triggers a signal when an item is in the funnel. This signal turns off a redstone flare which then deactivates a drive rail. When the goods trolley arrives, it remains under the hopper until the contents of the hopper have been completely transferred into the goods trolley. A picture says more than any words:

There is an item in the hopper in the picture.The signal from the Redstone flare goes under the rails in the picture.
IMPORTANT: the drive rail MUST be pointing downwards, otherwise the trolley will no longer be
keep driving!!!