What happens to valuables that get lost down the drain?

LBC Studio

Mystery Hour Question 

What happens to valuables that get lost down the drain?
Patricia, Epsom  
If you are part of a small catchment area, there is a chance that your sewage will go to a small pumping station before being sent out to the broader network, there have been cases where people have called asking pumping stations to check. You could get lucky, if it’s a heavy metal it could sink to the bottom, or if it’s going through a small sewer with a small flow, the item can get caught in a manhole. 
If you’re in a city, on a major network, chances are, it’s never going to appear again, and if it does, it will be found by someone cleaning a sewer 20 years later who will think “Oh, brilliant!”
Sometimes these items will come up in the mechanical screens that are set up to take out larger debris and if you’re lucky the guys might spot it so you’ll see items on the side next to the screens sometimes, but no one really wants to pick those up.
If someone rings in, saying where they live asking us to look for their item, we’ll tell them that there is very little chance of us finding anything.
Luke, Poole 
Qualification: 18 years in the sewerage and water treatment industry, currently working for a water treatment company in the south west.