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.
https://www.amazon.com/Itron-100W-Communication-Module-ERW-1300-403/dp/B0DSJ1XD12 <-- It's this (or another model in that line). I zoomed into the image and could decode "ERW-1300" and Duck duck go did the rest.