There is a long, thin, rubber-y line wrapped around/connected to the water line pictured below.
Other angle:
The piece in question is loosely hanging via a zip tie on my main water line about shoulder height and can be moved up/down easily.
No idea, but it has a couple of barcodes on it. You might try scanning the barcodes and looking up the numbers that come up, one of them might be a part number..